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Bosch Tankless Whistling Problem

I have an Aquastar 250NG Bosch tankless water heater that won't stop whistling and it doesn't appear to be that the inlet line size is too small or the venting is incorrect.

From the research I've done, it seems that the valve needs to be adjusted. Has anyone done this and succesfully eliminated the noise? I've read about plenty of people having the same difficulty with this noise, but very few success stories.

I guess what I'm really looking for is someone who has personally beat this problem and the specifics on how to do it before I either spend the time adjusting the system further or hiring someone to come in and replumb or pipe the unit. If it's something that can't really be addressed, I'll just scrap the whole idea and get a new unit, but I'd really rather not spend the cash as money is tight.


  • Ironman
    Ironman Member Posts: 6,366

    Adjusting the gas valve is not something you should be attempting yourself. You could be creating a potentially dangerous situation for yourself and family. Or you could cause the appliance to fail pre-maturely.

    You need to find a good gas tech that has and knows how to use a manometer and combustion analyzer.

    If there's a regulator in the gas line within 10 lineal feet from the heater, that could also cause whistling.

    Get a good tech and have him call Bosch tech support from the job site if he can't solve the problem readily himself.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Another Mother Whistler...

    I have had numerous of them (nat gas fired aoppliances) that had been connected with too small a flex connector that would cause a whale to be jealous...

    Seriously, flex connectors set up a harmonic hum/whistle that will drive you nuts... Pipe it in rigid and watch (listen?) your problems go away.

    And I agree with Ironman, you shouldn't be adjusting anything unless you are capable and qualified to test flue gasses to amke sure there are no unsafe conditions present. It just takes on good exposure to CO to ruin your day. Make that LIFE.

    If you aren't capable of doing rigid pipe fitting, tehn maytell you should leave it to a pro. Natural gas can kill you too, In more ways.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • meplumber
    meplumber Member Posts: 678
    Great advice.

    We have a saying at my shop.

    "Oil wipes up.  Gas blows up."

    Call a pro if your not one.
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,186
    Oil blows up too

    I learned that the first reset hitter I went to work on. " Ma'am how many times did you hit the reset?" lady replies "only once then I called you" " WOOOFFFFF!" Lady then says " perhaps my husband hit it a second of third time"
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • meplumber
    meplumber Member Posts: 678
    Well put Charlie.

    I had an old American Standard a few years back.  the home was owned by the owners of a Chinese Restaurant in town.  The teenaged daughter was the only one of them that spoke English.  I asked the question.  He nodded, "Once or twice."  I touched it off and boom!

    Try once or twice every hour for three days.  Burned in the chamber long enough for me to clean out my van while waiting for it to stop.

    I will still take an oil boom over a gas boom any day.  It seems like I lose arm hair and eyebrows at least once a spring while starting up pool heaters.
  • Jack
    Jack Member Posts: 1,045

    The boom question is why I always look for the appliances clearances...then I look for mine. "How much room do I have behind me to get away from this thing?"

    40 yrs ago when I was a first year apprentice, we had a major flood in upstate NY. HUD trailers were sent in to house folks and I was piping the gas lines. the piping was no problem, but the furnaces with the "new Spark ignition" were, something of a mystery to me. That is the mildest form of understatement. Due to the boneheaded apprentice trying to get that furnace running and the splendid technology of the early spark ignition, I almost went thru the wall of that trailer trying to get away from the fireball that came rolling out of the furnace. It took my nice long beard and turned it into Rice Crispy's. Gave me a bit of sunburn too. It's amazing how smart I felt;)
  • JJBandMe
    JJBandMe Member Posts: 2
    Still Wondering

    To clarify because I'm still not sure based on the answers posted, there's nothing I can do to adjust this unit as far the temp to help eliminate this problem?

    I'm well aware that there is specialized equipment involved in order to adjust the internals and that piping may be the issue, but I also am aware of the fact that it seems like most the data on the web points towards a lot of trial and error, mostly error at the expense of the customers pocketbook and zero results.

    So if there's nothing I can do personally to eliminate the problem, has anyone had success getting this specific unit to quiet down in an application that was previously noisy or am I just barking up the wrong tree and should move on to another source of heated water?
  • Charlie from wmass
    Charlie from wmass Member Posts: 4,186
    JJB and ME

    not a lot of trial and error. Sorry we did get a bit off subject. You need a professional with a digital combustion analyzer. Call the folks recommended near you. Yes it will cost a bit to get it in order but there is not guesstimating this. It needs to be set properly with both pressure and air settings for proper combustion. If the installer did not do this to start with there may be other installation issues.
    Cost is what you spend , value is what you get.

    cell # 413-841-6726
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Simple test...

    It may not be a fire side noise issue. It could be a water side issue.

    Fire it up, and when it starts whistling, turn the gas OFF. If the whistling stops, its a fire side issue. If it continues, its a water side issue.

    It could be that your heat exchanger is limed up and in need of descaling. That will cause whining and or whistling.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
  • Giovanni
    Giovanni Member Posts: 1
    Bosch Water Heater Whistles

    I def have a fir side issue. When i turn a valve anywhere in the house full blast hot water only I get the loud whistle. I have flex tubing connected to the unit but not directly. I have about a foot or foot and a half of rigid pipe connected directly to the Bosch Tank-less heater and then the flex tubing to the rigid tubing. How long do you think the rigid tubing needs to be to stop the whistle?
  • lcruz
    lcruz Member Posts: 1
    I know that this is a very late response but others may be searching for a solution. I actually fixed this problem myself. The whistle coming from my unit could be heard around the neighborhood.
    All of the checking for technical issues around valves, tubing, gas pressure, etc. yielded nothing.
    Turn out that all that was necessary was lubricating the squirrel cage fan. I used a spray lithium grease - one squirt. Instant fix. It has been a year now and the whistle has not returned.
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