I wasn’t insane after all! (Bosch tankless story ends well)

This is a follow-up to my original post about our Bosch 635ES (250SX) water heater, which you can find here.

My first post was a recap of all the problems that we’ve had with this heater over the last two years. Tonight’s post is a very happy one. About 10 days after I sent my long email to Bosch detailing all the steps I’ve taken to remedy the startup noise issue, I finally received a reply. I had given up hope, since they promise responses within 24 hours and an earlier one I had sent months ago went unanswered. Imagine my shock when I read these words:

Hello Julio,

I am sorry to hear that you are having so much trouble with your water heater. I would like to offer a possible solution. Since you have tried to dial in the air/gas mixture to no avail, I think that we should swap your heater for a new one. Please call our toll free tech support line at (866)330-2730 and we can set this procedure up. I have updated your record to reflect this so any tech you talk to should get it going quickly.Thanks for buying Bosch.


I called the number right away, and the tech support person took only a few minutes to get me set up with an emailed warranty return number and return instructions. I called George Morlan, the local plumbing shop where I bought the heater in December of 2004, and explained the situation to the store manager. Even though he was unable to reach Bosch due to it being after 5 on the East Coast, he said they’d go ahead and swap it if I brought in the old unit. I went home a little early, pulled the old one down, brought it in, exchanged it, installed the new one, and….

IT WORKS!!!!!!!!!!!!

Looks like all the agony and gas line upgrades may not have been necessary. My opinion has undergone a complete 180, and my new mantra is:

Bosch tankless heaters are great!

I appreciate all the suggestions that people gave to help troubleshoot the problem, but it looks like we just had the 1 in 1000 lemon. When I think back to how many times I had to fiddle with the gas/air mixture setting on the old one, it felt amazing to have this one just fire up with NO tweaking. I probably took the cover off the old one about 20x to try to adjust it. It is better than the first unit a couple ways:

  1. No startup noise. None. I’ve noticed that it is even quieter than the old one was even at its best. On our ground floor directly above the heater, I can’t hear it at all. With the old one, you could always at least hear the burner fire up, or more commonly, the GRUNTING noise.
  2. More stable. The old one had a really difficult time handling low-flow situations. I always thought it was typical performance for a tankless, but this one is noticeably better. While you still need the 3/4 gal/minute flow rate to get it to turn on, the burner will still stay on if you then turn it down. I’d estimate that it’ll go down to 1/3 gal/min before turning off. Big improvement!

While I wish that I had been more aggressive with pursuing this with Bosch before now, I hadn’t had any other experience with tankless heaters and therefore had no good frame of reference. If I now had to go back to our old heater, I’d know it was messed up. My gut feeling is that all of my gas line upgrades were unnecessary. While they will allow the heater to get as much gas as it can eat, I believe this one wouldn’t have made the noise even with the 3/4″ line. On the bright side, who doesn’t want enough gas line capacity in their basement to be able to run a kiln, a restaurant and a glass blowing workshop, all at the same time?

In case anyone missed the morals of this story, they are…

Tankless heaters are great, if yours doesn’t work well, it may just be a dud, and

We LOVE Bosch!!

9/7/2008 update: After living with the new heater for another year and a half, we we revise our statement to say that Bosch tankless heaters are merely OK.  Every year at the peak of summer, the heater will have a tough time maintaining its temperature, and we will get blasts of cold in a shower.  My impression is that this heater is great for “full throttle” use, but it struggles with low to moderate flows.  Again, this makes we wonder if we would have ultimately been more satisfied with a smaller unit that would regularly run closer to its maximum output.

55 thoughts on “I wasn’t insane after all! (Bosch tankless story ends well)

  1. Congrats! Always nice to get stuff like that resolved, lest they do drive you insane.

    We’ve loved our Takagi TK3 tankless.

    And great name for your blog 🙂


  2. I’m glad to hear you had a happy ending on this.

    I’m still not sold on them the way I used to be but your post gives many hope and it’s nice to hear Bosch has such great customer service. You don’t see that much anymore.


  3. I keep saying, the hallmark of a good company to deal with is not that they never make a mistake, it’s how they respond when a mistake is brought to their attention. I’m glad that once you finally reached them they were so immediately and perfectly responsive!


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  5. Glad to hear Bosch did the right thing. Am looking into tankless water heaters … your stories are enlightening. As with any technology, it sounds like its getting better with age. Did going tankless actually help reduce water and energy consumption? Has it paid off? Or was it more of a green thing?


  6. It was motivated by being green. The tankless uses much less gas than the 20 year old water heater that came with the house, but I think the difference would be smaller with a modern, better insulated tank. Much of the energy savings will depend on how the hot water is used in your home. A common misconception is that tankless heaters inherently use less fuel than tanks. That’s not exactly true, since it takes a given amount of energy to raise the temp of a given amount of water.
    Where the tankless rules is in its reduction of standby heat losses. For example, if you took a shower in the morning and didn’t use hot water the rest of the day, the tankless would only kick on for your shower and shut off. It’s great when you go on vacation knowing that no gas is being used to heat a giant tank of water. A tank heater has to keep 40 or 50 gallons of water hot 24 hours a day. Even with good insulation, some of that heat will be lost and have to be replenished throughout the day. Also, many tank heaters have pilot lights, which burn continuously (that, of course, is an advantage in a power outage, but that’s a different subject) and use some amount of gas all the time. If you use hot water throughout the day, the standby losses would represent a lower percentage of total gas usage, thereby reducing the energy savings. One other factor that favors tankless heaters is that many tank owners crank up the temp to super hot and add cool water to bring it back down to a usable temp. The goal is the stretch out the number of showers that can be taken with hot water, but the extra hot water would create a higher standby loss (the rate of loss would be dependent on the difference between the hot water and the air surrounding the tank). With a tankless, you can set a reasonable temp, since it will keep pumping out that same temp for an infinite number of showers.
    A tankless will not save water vs. a tankless.
    Depending on where you live, some of the energy rebates and credits can really help offset the cost of a tankless (Oregon is great for this), but I never recommend a tankless to someone just looking to save money. The payback takes some time, and it would just be easier to buy the best-insulated tank that you can find. I would only get a tankless if your goal is to reduce fuel consumption for the sake of the environment, not for your wallet.


    1. Well Julio, in light of your response, I have owned a Bosch tankless (250 SXO LP) to be exact. Anyways, I had it since 2007 when I was tired of refilling the 100 gal. propane tank every 2-3 months with my old tank heater. But now, I have it filled up every 5-6 months. My Bosch has really saved me a ton $. I’ll never go back to a tank water heater. However, it has now been acting up on me and I just bought me a Rinnai in which I heard great reviews on it. So it’s on standby til my Bosch dies. So, to anyone asking bout switching to tankless, do your research first until you find the right one for your situation, then get it. I’ve had no regrets, especially when you’re saving lots of $ and helping the environment at the same time. One downside to it is that you may use a little more water depending on the situation. Meaning that if the heater is far from your farthest outlet point, then your water bill may be slightly higher due to that the heated water would take longer to get there.
      I also bought an electric tankless heater for another house of mine and it has saved $$ too.
      So by far, Tankless is a way to go!!!!!!


  7. I think the other way in which a tankless heater can be preferable to a conventional heater is in terms of space-saving. If you have a teeny space in which to put your water heater, it can make a big difference. Our laundry room is pretty tight as it is. With a large tank, it would be incredibly cramped. The tankless is only the size of a tall medicine cabinet – we have so much more space now (or at least, it feels that way!)


  8. Julio, you didn’t get the only bad water heater. I’m having the very same problems you had with the same unit, and I’ve also tried the exact same solutions, to no avail. I haven’t started bothering Bosch, but maybe I will soon. I’m encouraged to hear that they were responsive to you. I am an energy auditor and in position to recommend (or not) this equipment. Right now, it’s a “not” from me!


    1. We had the first unit replaced. The second one has the same problems. It’s been years of tweaking and we’re becoming tired of it.


  9. Charlie – we feel your pain! I don’t know which was more annoying – that wall-shaking start-up grumble, or the never-ending high-pitched whistle we had to endure whenever we ran the shower, dishwasher or washing machine!

    I really wish we had contacted Bosch sooner, because the replacement unit is dreamy – it works just as we hoped it would and it’s so quiet! Our neighbors don’t hate us anymore! You should definitely contact Bosch to see if they will offer you a replacement unit. When it works the way it’s supposed to, the water heater works quite well.

    Good luck, and let us know how it goes!


  10. We have the same problem (I think). We don’t have a big startup noise but we do have a high pitch whistle that is driving our neighbors crazy every time the hot water is used even for a second. The whistle really gets bad when the fan kicks in to high speed mode after the hot water is shut off. The plumber is here now to alter the gas/air mixture, but based on your story I am not optimistic that this will solve the problem. I’ll keep you posted.


  11. Hopefully he doesn’t fix it by creating the startup noise! Your issues sounds a little bit different, since ours only whistled while the heater was running. Once it stopped heating, the whistle stopped, even if the fan was running.

    I also want to add that after living with our new heater for 4 months, we have not had any problems at all. Not one. Every few weeks once of us will say “remember when we used to live with that awful noise?” We did put up with it WAY too long, and it’s so pleasant to have one that does its job without arguing with us.


  12. Julio –

    We have had one of these for a year, ordered it by mail and had it installed by a local plumber.
    Our problem is the EC error code. We get it all the time especially during the summer. (Humid north carolina ? )
    We also get the wisle noise but just on cold winter days when a log hot shower is taken.
    My question is how do you “adjust” the unit?
    I did not see a place to do it.

    Thank you,


  13. The manual is here.
    See page 32 of the manual. It’s not for the faint of heart, and you could easily make it worse if you don’t keep really close track of the screw’s original position. Good luck!


  14. We bought one of these bosch heaters and paid a big money to get it installed by the city. We didn’t turn the water in our house back on for months because it was being renovated. We finally turned our water back on and the heater simply won’t work. We had the city come back out to check it and they said that it’s not going to work because the city water doesn’t have enough pressure. Help!! We have no idea what to do and we’re out of money. The heater is a Bosch. it’s the kind that doesn’t have a pilot light and doesn’t use electricity. Supposedly, the pressure generates it’s own spark each time there’s a demand for water heater. We had it installed eight months ago. The city never even cautioned us about the possibility it wouldn’t work. Is there any cost effective solution? I don’t know if we can afford to rip it out and get a normal water heater. Someone told me there’s such thing as little booster pumps for pressure we could install in the cold water pipe feeding the heater. Is that true? How much is it going to run? This is really stressing me out. Any advice?


  15. Bonnie,

    I have no experience with boosting water pressure. I know the pumps are available (google “water pressure pump”), but by the time you add up the pump plus the install cost, it’ll probably get really expensive.

    You might be better off just selling your Bosch and buying the most efficient tank heater you can.


  16. My recently installed Bosch 1600P is a thing of beauty to behold. The only problem is that it will not provide hot water. Oceans of warm water are however instantly mine (till winter.) This unit is marketed as a whole home unit promised to deliver unlimited HOT water for a single application at a time. It does not. From all I can figure this thing will only make hot water if you have a flow rate equivalent to a small boy writing his name in the snow.


  17. Julio, I am now a Bosch tankless believer as well. After my earlier rant I just couldn’t give up and let all the jabbering nay-sayers be right. I found that if you take the cover off this thing (my 1600P from my earlier diatribe) you can seriously over-clock the temperature control knob from the stock position, to where actual hot water is available, buckets of it! This was nowhere in the instructions but it worked for me. Now it truly is a thing of beauty to behold.


  18. Rob, glad it worked out in the end!

    Sometimes I think we should have bought a smaller one like your 1600, because we don’t run 2x showers and rarely run the washing machine while showering. We have noticed that our otherwise perfect heater struggles in the summer to not overheat the water (at least this is my hypothesis). During the warmer months we’ll eventually get a surge of hotter water, followed by the ice cold blast that only tankless heater owners can relate to. Once September came around, the problem resolved itself.

    I need to find a permanent solution to this, although there’s no rush now that it’s cold out. I’ve between now and June to come up with the answer…


  19. Julio, THANK YOU for posting this on-going story and keeping it up-to-date. I felt so alone, like a dissident in hiding, until I found your posts.

    I installed a Bosch 2400E in our home. Our concerns, choice, and installation issues mirror your own. No professionals in our area are experienced with these units at all, so paying them to guess there way through it didn’t make sense; and paying a product experienced gas-rated plumber to drive 60 miles (each way)… well, the vault doesn’t contain that kind of money. The owner of the local plumbing supply house (the only place to get 1-1/4 inch black pipe, fittings, & shut-off) thought I was crazy. But I didn’t want to get the unit operating then be left wondering about the gas volume, so I opted to install the larger black pipe. Like you, I felt Bosch is correct that short reductions in pipe size won’t affect supply. Everyone (including experts) tried telling me that the city only supplied gas on 1″ lines anyway, but that is not true. In the US most gas utilities install 1-1/4 (ID) to the meter. The 1 inch pipe or CSST occurs from the meter into the house, usually no more than 3 feet.

    We’ve experienced the sudden shutoff you mention, but it was corrected by following Bosch’s reccomendation to turn down the temperature setting. My wife’s (dish pan) hands could take blow torch heat, but in the shower she is easily scalded. I’ve had to ask her to get her hands and body together to accept a lower sink temperature. The wireless remote for the unit would be nice, but at $160+ is out of the question (I spent all our extra money on the stainless steel venting). At what temp do you guys set yours? Bosch says no more than 120, and there service bulletin TWH-G2-02 (Overcoming temperature fluctuations) says “Most people use hot water in the range of 100-110F”, which (coming from tank heater usage) I wasn’t too sure about until I read that solar water heating units generally heat water to 105. So, I set ours to 110 (down from 120) and it seems to have cured temperature fluctuation problems.

    There have been some really annoying repairs to be made (again by me, as warranty doesn’t cover “expert” service). I opted to repair rather than return because the issues seemed more easily resolvable than yanking the unit down. The felt “gaskets” under the front cover, which seal in the heat exchanger and flue collection, had gaps between the strip ends, and one strip corner came off with the cover. It seemed like exhaust gas was getting into the basement. I filled in the gaps with high-temp silicone and put in another layer of “gasket” material. Upon close inspection, it was easy to spot other areas (box corners) that needed silicone to seal off this chamber. The gaskets for the air intakes are too thin for only three screws and can leak in the spaces between the screws (silicone again).

    This seems to have worked. It really annoys me that I had to “repair” these extremely important little things on something with such a large price tag. One thing that is hard to get used to is the smell of superheated air in the basement after the unit has been running high performance. The exhaust pipe runs 12 feet in the basement before going out, and gets VERY hot. It cools quickly, but it scorches the basement air quickly. It smells the same as when an electric stove top element heats up. I could easily run it up the old chimney flue, if I were Warren Buffet;)


  20. Thanks to all for your various posts. I too am experiencing problems with my new 2400e. Hopefully someone sees this soon and has some thoughts.

    Ok, so here’s my story. I’m actually a Bosch employee (different division, I’m in the automotive side of the biz), so when my old tank water heater started leaking at a slow drip pace I started looking into tankless models. I use hot water infrequently, just a shower a day and a load of dishes 1-2 times a week, maybe a little bit at the kitchen sink from time to time, so the energy savings sounded like a good incentive, and the tax credit was still in effect. Also, as a Bosch employee I was able to get a discount, knocked a little over 20% off the best retail price I could find. I compared against some other brands but with the discount the Bosch 2400e won out. Also, I know from experience that Bosch has high quality standards in their other products. So I ordered it (had to order over the phone for the employee discount, came shipped 2nd day air). Then the fun began.

    First problem, unit arrived, but was a natural gas model, not the LP I ordered. Called cust. service, kudos to them, they acknowledged my order correctly indicated an LP model and that the warehouse screwed up, sent out an LP model the same day. (I was worried they’d want me to ship the NG model back first before sending the new one.) Ok, mistakes happen, they had great cust. service, no harm no foul.

    I was taking my time at getting the install done because of other priorities, but was able to spread the work out over a few weeks because I chose a new location for my water heater for a few reasons. Current heater is electric, new one is LP, so had to run gas line and exhaust/intake lines, and wouldn’t have been able to do all that in a day, didn’t want to remove the old heater and be without hot water for a long time while working on the project here and there in the evenings. Also, the new location in my crawl space required much less of the expensive stainless steel exhaust pipe, saving ~ $200, plus located the unit directly under my kitchen sink for a fast response time in the kitchen where you’d be most likely to want small, quick amounts of hot water (unlike a shower), and distance to bathrooms was about same as location of old heater.

    Was almost done with installation, only had gas line left to run, when the old heater finally suffered catastropic failure and is now out of service (ok, my bad for being slow on the acquisition/install process). Made a frantic effort to run the gas line that night (the outdoor portion of which I had to work on in the rain, of course), next day propane company pressure checked the line (no leaks, measured 13″ H2O at the regulator). Note: despite only having to run a total of ~ 20′ of line with 3 elbows and a T, decided to go with 3/4″ black iron to leave no doubt on capacity, plus leave room for possible expansion for a gas stove on the same line. This is far far below the spec. limits for max length of a 3/4″ line.

    Tried to fire up the unit, could never get anything but the EA code, even after purging air out of the line and verifying pressure at the unit’s pressure tap. (ok, I could only scrounge up a 0-10″ H2O manometer, but it easily pegged the needle on the max. stop of the gage, which appeared to be around 11″, which is the min. limit for the unit).

    Had to wait till next day to call tech support (since they close at 5 ET). Called, after 1hr.+ on phone (25 min. on hold, 5 min. with 1st level tech support, ~30 more on hold for 2nd level tech support, and another 5-10 min. talking to them) they concluded my gas valve was not opening properly. They pretty quickly concluded they’d send me a new unit. Again, they didn’t hesitate to send the new unit without waiting for me to return the one I had, so again kudos to them. Ok, so I’ll grant them another mulligan. That was a Friday, new unit couldn’t ship till Monday since it was already >5pm by this time, so new unit to be in on Wed.

    Wed. – no unit. Called to ask for tracking #, they discovered unit never shipped, apologized profusely and said they were overnighting the unit to arrive Thurs.

    Ok, Thurs., unit received. I already had the first one out, so I put the new one in (quick job when everything’s already plumbed and ready), fired it up, and I’m still getting the EA code. This time, however, I can hear the gas valve opening and closing and it’s sparking just fine, so theorized I had air in the line to purge out after my reinstall. Did some purging and finally started getting unit to light up, followed by flame going out after 1-2 seconds. This repeats until the EC code shuts it down.

    Next day did more purging of line, finally able to get unit to come on and stay one. Had it running consistantly, starting and stopping just fine, everything seemed like it was finally working correctly. ~ 1/2 hr. later, tried running faucet again, no hot water. Crawled back down there again (the added annoyance of choosing to locate unit in my crawl space) to reset the unit and clear the error code. Took a few times of getting and resetting the EC code and again it seemed like it was working. Ran the dishwasher, everything was fine. Next morning, not working again.

    Spent some time watching the flame through the window as it lights up, burns, and goes out prematurely to watch the dynamics of the flame. It almost looked as if the flame was being blown out. Theorized that since I’d been working with the cover off, that perhaps the lack of drag on the exhaust vent blower might be causing too much air flow and that the flame actually was being blown out. So, I put the cover back on (but still without the intake air pipe connected, just the intake port at the top of the unit), thinking that if the intake air had to be drawn through the 3″ opening there’d be more drag on the blower moter and thus less air flow to blow out the flame. Unfortunately, that didn’t make any difference. I went ahead and connected the rest of the intake air pipe (it only runs about 4′ plus 2 elbows), even though the unit is rated to run off of room air and this shouldn’t make a difference, but I tried it anyway. This still didn’t make a difference, I still keep getting the EC code.

    Now been over a week since I had hot water in the house, and now I have guests in town. I showered at the neighbors house all last week, but this is getting annoying. Of course, it’s the weekend, so no tech support till Mon. I’m still searching for the solution to the EC code. If all else fails, I’ll be back on the tech support line on Mon., but in case anyone sees this and has some ideas, please let me know. Sorry this was so long, but figured more details might help spark the most relevant ideas.

    Also, one other comment: the more I read some of the posts, the more I am wondering if I’ll hate the .8 gal/min. min. flow requirement, as sometimes I like just barely warm water or low flow rates. For those with a 2400e or 250SX (it’s predecessor), do you find yourself having to run the sink faucet during your shower just to get consistent showers at your desired temp. a lot, or is it like Julio said that you can go down to a lower flow rate after the unit fires up? Or, is the solution simply to turn the set temp. down lower to say 105-110F so that your single-handle valve is using a higher percentage of hot vs. cold and thus keeping the flow rate above the min.?

    Any thoughts?


  21. Gene,
    Wow, sounds like you’ve got your hands full with yours, and you’ve certainly already poured a lot of effort into this project. Reading the list of causes for the EC code, I’m going to go out on a limb and say that the gas valve in your new unit isn’t working right. It sounds like you’ve ruled out gas pressure as being the cause.
    And in regard to the temp vs. flow rate issue, I still don’t feel like I’ve fully solved that one. I sometimes change the temp on the heater seasonally, as it seems to respond differently as the incoming water temp changes. We also have a pressure balance valve that may be screwing things up, since you really don’t need the same valve behavior or protection when your hot water is only around 100 degrees. I’ve also thought about temporarily removing the restricter in the shower head in order to see if that gets the heater to be more stable. I don’t want to waste the water with every shower, but it would be helpful to see if suddenly the heater works perfectly when the flow rate is higher. Although @ 2+ gallons per minute, it should have no trouble staying in its zone. I never finish working on it, though, because once I get things settled with a temp change, I get lazy.
    Good luck with your problem!
    You may have seen all these already, but I’ll post them anyway in case someone else hasn’t seen them. These came from the 250SX troubleshooting page:
    1. Wrong gas type. Verify gas type indicated in rating sticker located on the heater’s right-hand side, coincides with the gas type you are using. NG is a natural gas unit and LP is for liquid propane.
    2. Loose connection to the flame ionization rod. Verify that the thinner yellow leading from the control unit is securely connected to the set of electrodes located at the bottom right-hand side of the heat exchanger.
    3. Flame rod is dirty or damaged. Failure to vent the water heater in accordance with the specifications in the installation manual may dirty/damage the flame ionization rod. Contact Technical Support (800) 642-3111 to see if replacement is necessary.
    4. Low gas pressure. Inadequate gas pressure will put the fuel-to-air mixture (CO2) out of adjustment. This will result in an unstable burner and lifting flames. Ensure gas pressure is in accordance with specifications in the installation manual. A gas pressure reading is needed to proceed further. Contact your original installer or a local certified gas technician to obtain this reading. See: TWH G2-03 Checking gas pressure.
    5. Air-to-fuel mixture (CO2) is out of adjustment. Verify CO2 reading. CO2 adjustments can only be done by a certified gas technician with a calibrated Combustion Gas Analyzer. For proper CO2 ranges. See: TWH G2-12 Measuring and adjusting CO2.
    6. Gas valve or flame ionization rod may be damaged. Contact Technical Support (800) 642-3111 for further instruction.


    1. Hello Julio,

      I installed my 250sx-ng in 06 with a 1″ flexible dedicated gas line from the meter. fresh air intake and the extra water filter/softener that I can screw on and off before the heater in 3/4 copper supply. I only have one issue.
      My main issue is in the kitchen, we get hot or cold and when trying to get warm for rinsing dishes it goes to cold only. Most of the time it will shut down and I have to reset. I want to purchase the remote temp controller for about $150 but thought I should check to see if there are any problems with communication between the remote and the heater. Input regarding this issue would be welcome for I plan to purchase the remote very soon.

      Thank you.



      1. Leslie, we have no experience with the remote control, so I can’t comment on it.

        We had a similar issue in that this heater is horrible at dealing with low flow applications. The intermittent nature of washing dishes makes the problem even worse. We would end up having to waste a lot of water (much of it partially heated) to get hot water at the kitchen sink. We finally gave up and installed a mini 4 gallon tank heater under the kitchen sink, which took care of the problem but was counter to the ideal of not heating water 24/7.

        I have not posted this yet, but our mini tanks (we had two) recently started leaking. We opted not to buy another and are instead installing a small electric tankless Rheem heater. I just installed one for the bathroom sink, and it works great. It will heat at pretty much any flow, as long as it’s above a trickle.

        My opinion is that the Bosch is only useful for showers or the washing machine. It’s a joke when it comes to washing hands or dishes.

        More to come soon on the new electric tankless heaters…


  22. Julio,

    Thanks for the reply. Well, there may be some good news, at least for now, but I’m not counting my chickens yet.

    So yesterday (Sunday) we were all in need of a shower and I didn’t want to bother the neighbor again, so I told my parents who are visiting from out of town that I would go down in the crawl space and try to get the unit reset and running, then stay down there and watch the unit while they tried to take showers so that I could reset it immediately if it faulted out again in order to prevent anyone from receiving an unexpected blast of cold water.

    It took me ~ 10-15 minutes of the unit flaming out, trying again and again, generating the EC code, resetting the unit and repeating the process, etc., until the unit would finally light and stay lit. So they took a chance and each took turns in the shower. During the entire time, I only saw the unit lose flame once, but it restarted on the first try and did not fault out. Since it was getting to be dinner time, I didn’t take one myself right away, but intermittent use of hot water at the kitchen sink before and after dinner continued to work just fine.

    After dinner, I tried firing up the shower and it seemed to be working properly, so I hopped in and was relieved to have a nice, consistently how shower. I even tested the hot water again before bed and it was still working. So far, the water heater has continued to work all day today (Monday), including a quick test just a minute ago. Knock on wood, maybe I’m over the hump and my troubles are behind me. While I can’t explain why it would be, I am wondering whether the unit just needed a good sustained “burn-in” to get the burner, combustion chamber, gas valve, or some other component(s) to consistently function correctly.

    Have you or anyone else reading this experienced anything similar?

    Thanks again,


  23. I have a long history of trying to work with your Bosch Water Heaters due to my Aqua Star 250SX NG. We have recently learned from their recommended plumber that the water heater we have has rust in the gas valve. There are no assurances that it will ever work correctly even when installed “in accordance with the printed instructions provided”. This is customer fraud. Bosch Water Heating manufactured, marketed and sold me a gas water heater that Bosch Water Heating knew will not work as promised when installed according to the provided instructions. After further contact with your technical support staff, I was never told of the problems due to the vent piping that can occur when installed according to the provided instructions. The installation of two elbows and a secondary condensate drain was suggested by the plumber yet it has no manufacturer approval. The plumber recommended by Bosch Water Heating to replace my gas valve showed up to inspect the installation and charged me for that inspection, no repairs were planned or are currently available that will correct condensation build-up in the gas valve.
    I am requesting from Bosch Water Heating a solution to condensation in the gas valve, swap my current Aqua Star 250SX NG for a new one due to the damage seen by the plumber and the assurance from Bosch Water Heating that the Aqua Star 250SX NG has be field tested and will work correctly when installed “in accordance with the printed instructions provided”. The possibly of me paying the plumber $300 to $500 to install a gas valve and vent piping with no assurance that this will resolve the problem that we have had since the installation is insane of Bosch to request of us give our current history with them.


  24. So many little details that Bosch leaves out!

    I have had a 2400ES since November (8 months as of today) and have had similar problems as above and the other post. I am in the early stages of trouble shooting but I am not very optimistic about it after reading everything.

    First, the hot/cold fluctuation it horrible! My current shower (I did a 100 sq ft addition and master bath is not done) is about 70-75 ft of line away from my heater and it takes over 2 minutes to heat up. Once in the shower, it will turn cold and back to hot 2-3 times during the shower. My HATES it! It is ok to me but still sucks. I tried running the sink faucet while taking a shower thinking it ensure enough gpms: same thing. My heater is about 60-60 ft away from the meeter and have a 1″ line half the way and 3/4″ the rest of the way. I have enough pressure but want to change the line to 1″ all the way. I know the installation instructions say for this distance, I need 1 1/4″ line but don’t want to go that big. Especially after reading up today on this site and others. I also go the same responses from local HVAC guys when I told them I need this big of line.

    Second, is the whistle. Mine is more like a siren as another blogger said. I was messing with last night and it would change for seconds but never go away. I adjusted the vent, making sure it was secure and did not have leaks. I also removed and reinstalled the intake (mine is installed in a 2x car garage as a open space)line, adjusted it, and munipulate the intake thinking this would effect it. I was on the right per Bosch but it didn’t make a difference. Same siren noise. Mine “farts” too but this only lasts about 2 seconds on start up and I can stand this.
    It is warming up here but during winter the tap water is in the low 40’s if not below. I had the temp set at 134 degrees but lowered it to the default, 122. I will try a lower temp to see if there is a difference with the two things about. I would seriously consider selling my unit for $400 right now and go back to a tank. The life style change with having a wife and 3 kids and the long runs for water is a serious turn off!
    I will get back to you guys on this.


  25. Eddie,
    It sounds like yours really has some issues. There is no excuse for these heaters to cycle during a shower, since even a low-flow showerhead should easily exceed the minimum flow rate.
    I think turning the temp down may help you, though, because it will force a higher flow rate through the heater. Ours is set at 112, and that works out well. I think Stephanie runs the shower with only the hot water, while I’ll set about an 80/20 split between hot and cold. Either way, we don’t have problems with it cycling since the heater was replaced.
    Based on my experience I think your line is probably sufficient. If I had a lot of extra time on my hands, I would try downgrading our line back to 1″ or even down to 3/4″ just to prove whether or not a “good” heater could work with those underdimensioned lines. But of course there’s no way I would even touch our system, since all is good now. I’m sure Bosch’s recommendations are valid for running at max capacity, but I can’t believe that you need 1 1/4″ line just to keep it from making noise!


  26. I have to say these machines are for a person with quite a bit of mechanical ability. My background is a electrician. I talked my father into a upgrade since the old hot water tank heater was leaking. He looked at the tankless at the home depot and liked the idea. Well I found a new one on Ebay, from a local seller which was lucky because I met him for the pick up of it. The bosch 250sx was new and still in the box. I proceeded to install this. I did my homework, checked out the bosch install site, plus others. The copper lines had to be rerouted to the wall. the gas line was 1,1/4″ Trunk line to a furnace and the old water heater used a 1/2″ line. At first I had no problems with the copper lines I used 3/4″ and added 2 shutoff svalves, and one nock suppressor on the incoming cold. Also I added two hose valves for draining the system in maintenance or repair needs then put the last upturn of copper lines as a removable unions for removal and access to the small screens in the base of the water connections. These need to accessed every so often. So I made it user friendly for the future maintenance. I also did this with the gas line which was hard piped in 3/4″ iron. I used a fresh air pipe which was galvanized, and is a 3′ to 4′ system horizontal about 3′ total in length. I used 3″z flex stainless steel in a horiz through a block wall which is 7′ or so in length. It has 3 90s and a extra horiz condensate drain. The extra condensate drain is now speced on service bulletins. Ok at first I used the 1/2″ gas line with a flex pipe, and exhausted into the 3″ old chimney vent so I could use it the same night and it worked. No noises near perfect without the proper exhaust and gas line size. But then we would get the error code EC frequently, usually only for my dad in the shower. LOL So that’s when I changed the gas line to 3/4″ rigid pipe. It turns out that there is a 3/4″ certified flex gas line sold at cinnabar. I found that out after I did the hard pipe. Still got the EC error code often and usually for my dad. Now the house is equipped with single valve faucets which are not the best choice for these systems. We called moen and the sent us six new cartridges to change free of charge. Great, they are aware of this problem. But we still got the EC error code. and Yes usually when dad was in the shower. Now running the sink would help and mom and dad did this to help. I even put a brand new faucet in the sink and the shower for them trying to remedy this EC code.I also did finish the exhaust with the z flex. Still the dreaded EC code. Well I had spoke to bosch a couple of times by now, and tried some of the advice along the way. Eventually I spoke to one tech that just was a cut above the rest. He had me check the software #. You turn the machine off then on and read the first #s that appear mine said af 30 03. Well he said that was a defective computer board. It will work but is touchy with the single valves and who knows what else. He actually sent a new computer free. I put it in and she fired right up. We will be watching over the next month or so to see if this is the cure. Also the bosch tech said that bosch will not honor the warranties of purchases made through ebay/amazon/any none dealers. So to save a buck might backfire later. They honored my fathers purchase but didn’t have to. Dad even had the paperwork and orig warranty card which he had mailed in. All I can say is that it was a really nice technician on the phone that day. Now we are trying to get the remote to work. I installed the pcboard inside. But when I try to activate the remote addressing process it doesn’t work. You turn off the power then turn it back on holding the minus button, and it is supposed to bring up a rotating # for the remote s address. But no rotating # ever appears. It just acts like it has no pcboard in it and moves the temp down. HELP! Has any one encountered this problem? I will be calling bosch soon and I will follow up. Overall I like the thing and it does work, but its only good if you can tackle the project on your own. I would have to say there is a lot of extra work almost a extra 2k$. If dad would of had others installing this. So be sure you want one. This was all for my dad and mom. At my own house I just put in a standard water heater LOL. Maybe electric models may be less trouble some?


  27. Hi Dale here owner “Tankless Hot-H2o Systems” Just browsing !!! Id just like to comment on Bosch & say there not My favorite equipment,I have replaced about 40 or so in the last 5 years. Rinnai & Noritz are My top sellers & I dont get call backs. Anyone looking for a Pro install in the Chicago metro area? Just give us a call 847-546-8841


  28. Tired of Bosch, and cold showers. The Bosch 425HN may be fine when it works, but “forget it”. 3 years of going from “hot to freezing cold”, has got me weary. Nothing helps the problem. Bosch couldn’t care less. Its always my; fault in their eyes. I’m disgusted, and would never own another Bosch product.


  29. I posted a comment on Mar 22, 2007. Bosch has sent me a new unit with the vent pipe attachment that I needed. They back their product 100% even after 27 months of use.


  30. I purchased a Reconditioned Bosch 2400E NG from CPO this winter. At startup it kept getting an EC error. A local plumber got into the Combustion Valve and found it contained rust. Bosch sent him a new valve to install right away. No more EC codes.
    I have still to deal with a loud whistle when the burner first ignites. It only lasts a couple of seconds.


  31. I have nothing but disdain for the Bosch 250 I bought with the illusion that it would be just as reliable, just like the tank water heater, only smaller and save gas and water. I have had nothing but problems and have grown to expect one of 2 things when I get into the shower: Cold water and an EC error OR hot water and then cold water, accompanied by the EC error or not, just random periods, brief or long, of cold water. This is every shower. This is probably the most expensive piece of junk I’ve ever bought.


  32. Thanks for the detailed info here and glad to know others have the whistling/ringing issue and have had some success resolving it. It wasn’t clear to me where one would find the details of making the gas valve adjustments on their own. I’d like to try that first before waiting on hold w/ Bosch to ask for a replacement. Can you tell me where to find that info? Thanks.


  33. I’m glad I’m not alone. My Bosch has been a real let down and no one knows how to fix it in a city of 100,000. Cold bursts of water have turned me from a shower taker into a bath soaker. Not so great when you’re in a hurry. Everytime I use the dish or clothes washers there is a loud vibration noise. As soon as I can afford it I’m going to replace it with an old fashioned tank water heater. I think it is rare to find anyone in any of the service industries in the USA who is all that well trained any more. If you live in Germany it’s probably a well functioning unit as their service techs have far better training.


  34. I am sorry to say I bought a Bosch 1600H and I get tons of warm water in the winter and hot water in the summer. I have tried many different ways to correct the matter from calling the support team at bosch to going to the basement and tearing it a part myself. With my working on the unit I have a better understanding of how it works but it is not fixed. The customer service at Bosch tells me there are no complants on there tankless hot water heaters I am the only one. I wonder why it takes over 30 minutes to get through to the teck. I still though do not understand how Bosch sells their product at a do it yourself store, bought it a Lowes and installed it myself, but the teck said he could not talk to me unless I was a certified Bosch installer. I can not find anyone in a 100 mile area to trouble shoot it and they can’t tell me of one to call. Oh well what to do now just complain. The last one, the 2500, only lasted 6 years and they wouldn’t back that one Lowes did. So this one does not look like it’s going to last and well be replace in probably 5 years.


  35. Well the first thing you will find out is that most people commenting on how to fix anything have little to no idea what they are talking about. I have two Bosch tankless heaters. If you have problems with one the first thing you do is check the end of All faucets for trash in the antisplater devices. Then clean your shower heads. Then clean the filters in the input hose for your clothes washers hot water hose (check both ends of the hose) and the one in your dishwasher if it has one. Then take off the COLD water entrance pipe for the Bosch tankless and look up inside the heater cold water entrance and pull the filter out and clean it. You need a small hook device to pull it out.

    Then go to each faucet and see if the hot water side will fill a quart jar in 20 seconds or less. That is the amount needed to light the heater. Assuming your heater was installed correctly it should be ready to operate. If it does not you have a problem in he unit.

    Now you need to go to the Bosch site on the net and get the Service Bulletins on your heater model from Bosch. The water valve is a simple device that measures water flow and automatically adjust volume. It frequently is corroded. If you are adventuresome you can easily clean it. Turn the cold and hot water off and put a pan under the heater. Open the pressure relief valve momentarily to let the pressure off. the valve is a black plastic device with a little motor attached to it. Unplug the wires to the valve (two plugs) then look at the clips tht hold the valve to the pipes, note how they are fitted in the slots.. Then pull the clip at the bottom and top of the valve. Remove the valve and do not lose the o rings that seals the valve to the water line. unscrew the motor from the valve and lay it aside. Measure how far the brass splined shaft sticks out and then remove the valve screws. Pull the valve apart , do not wipe off the waterproof lube on the splined end of the valve. if the valve is corroded clean it with scotch brite but do not scratch the o rings, carefully take them off if needed. Carefully rub the lube arond the plastic threads and reassemble the valve. Put it back in making sure that the o rings and clips are in place properly.

    Make sure that the yellow high voltage wires are still clipped to the burner and separated from each other and piping. Reset the error codes by holding the reset button in five seconds. The gas and combustion air are adjustable if you read the service bulletins. you need a combustion gas analyzer to get the proper setting. The high frequency sound is coming from the burner. Moving the gas valve adjustor just a fraction will stop it but it is hard to adjust. READ THE SERVICE BULLETINS


    1. William,

      Your comments and procedure are very thorough. However, I don’t think it is accurate to just lump everyone’s problem into the “they don’t know what they are doing” category. One should not need a combustion analyzer to get a brand new water heater working properly. In our experience, the first heater could not be made to work correctly even after dozens of attempts. The replacement unit gave us none of the noise problems. Ever. On occasion it will turn itself off briefly during a shower, but that’s not too frequent (and that’s at a flow well over the minimum required). Even though we hired a “certified” plumber to adjust the first unit, even he couldn’t get it to stay quiet for more than a day. Since we had completely different performance with the same plumbing and gas supply, I stand by my assertion that some of these are poor performers.

      At best, the Bosch heaters are finicky. At worst, they’re defective. I just don’t see these kinds of complaints out there for the other brands.


  36. Our Bosch Aquastar 250 sx ng just caught fire! If we weren’t here it would have burned the house down. We had to throw a bucket of water on it to put it out. Why would they have flammable material in the heat exchanger? It was installed 6 years ago and was a problem right from the start. It would turn hot and cold in the shower and turn off unless the hot water was turned on all the way. This is the biggest piece of junk I’ve ever owned.


  37. If this is your first tank less water heater here is a few things you need to know.
    Is the flow rate lower than the flame rate on the water heater?
    All new tank less water heaters need to be adjusted with the help of a gas flame analyzer to prevent noises and flame outs. Its set pretty close from the factory but its not right.


  38. I have an AquaStar GWH 1600H NG. When I turn the temperature adjustment knob, the flow rate never changes. It appears to be opening or closing the flow rate never changes. The flow rate is at the maximum and the water is too hot but when we try to add cold water the flow rate drops and the water turns cold. Has anyone had this problem?


    1. They only use whatever it takes to run the electronics, which I would imagine is very little. I’ll throw my kill-a-watt onto it sometime to see what it uses, since I’m curious now.


  39. I installed my Bosch Aquastar 250 SX in 2004 and have had nothing but problems ever since. It has been high maintenance appliance I am constantly flushing the heater core, getting the air-fuel mixture adjusted by my local plumber.
    I am a contractor and remodel a 20 unit apartment building about the same time we use both Tagaki and Rinnai On- Demand Water Heaters. To this day I have not had one call about unreliable service, yes we did have to up size some gas lines add circulating pump to accommodate for long runs, but all in all the landlord has been very happy with their performance. Not to mention the other units I’ve installed with other homeowners.
    I would never purchase a Bosch Again. It is now a Saturday night and our water heater is on the blink again. Guess what Ill be doing with my Sunday. Replacing my 11 year old water heater! Don’t by Bosch


  40. Want to hear something even more crazy about BOSCH. We’ve had a model 2400e NG since October of 2007 and today, we continue to re-set it when it fails to start-up. When it was first installed, it didn’t work at all and BOSCH sent a replacement. Not long after that installlation, we began getting error codes ranging from C something to E’s. I don’t even pay attention anymore. Odd thing is, summer is the worst. I believe there is some sensor in the unit vulnerable to temperature or humidity changes. If I have the basement vent open when wanting to get some heat in the basement, the heater will not run until you close it. I believe the de-humidifier in summer plays a role also. It works pretty good once the furnace season starts then we forget about the frustrations until summer. So we’ve put up with this for nine years. Our first mode of operation is to go down the basement first before turning on the hot water. Just writing this makes me wonder how crazy we are, but the outlay of cash to get this installed the first time was more than enough and we just deal with the problem of re-setting. More and more frequently however, re-set button isn’t doing the trick. If you shower then want to run the dishwasher right after, it just doesn’t want to reset. If you wait a half a day, it seems to work on the first re-set. We are patient people for the most part but I believe BOSCH should have recalled these years ago and threw in the towel. My first clue should have been when I saw back in 2007 that they came out with a remote control to reset. Why would I outlay more cash for a product that doesn’t work as advertised. I like the idea of a tankless water heater! One that works would be IDEAL! We have asked ourselves many time about replacing this one but are a bit afraid to do so! I don’t trust the reviews, because if I recall, I bought the BOSCH based on positive reviews nine years ago.


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