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Thread: Tankless Water Heater white powder build up

  1. #1
    DIY Junior Member cpthook's Avatar
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    Angry Tankless Water Heater white powder build up

    I have had a tankless water heater for about 4 years.. I love it but it is constantly building up a white powder inside the flame area. The powder corrodes the flame sensors so every month or so I have to pull of the cover, blow out the powder, and use sandpaper on the sensors I can reach.

    The company can not explain what the white powder is. I have had a heating and cooling specialist out a few times and he says it is something in my propane. I called my propane company and they said it isn't their propane or anything they put in the propane.

    Does anyone else have this problem or have any idea what this powder might be or how to stop it from building up like this.

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    DIY Junior Member DaMan's Avatar
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    Quote Originally Posted by cpthook View Post
    I have had a tankless water heater for about 4 years.. I love it but it is constantly building up a white powder inside the flame area. The powder corrodes the flame sensors so every month or so I have to pull of the cover, blow out the powder, and use sandpaper on the sensors I can reach.

    The company can not explain what the white powder is. I have had a heating and cooling specialist out a few times and he says it is something in my propane. I called my propane company and they said it isn't their propane or anything they put in the propane.

    Does anyone else have this problem or have any idea what this powder might be or how to stop it from building up like this.

    That white powder is Calcium buildup. All that means is your city water has a hard water, or high mineral count. It is very common. When your tank less water heater heats up the water, the water releases all those hard water compounds and those compounds attach themselves to what ever they can. If you have the money, install a water softener.

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    In the trades Dana's Avatar
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    Somehow I don't think the water is coming in through the gas lines to foul up the flame sensor...

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    DIY Junior Member cpthook's Avatar
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    Quote Originally Posted by DaMan View Post
    That white powder is Calcium buildup. All that means is your city water has a hard water, or high mineral count. It is very common. When your tank less water heater heats up the water, the water releases all those hard water compounds and those compounds attach themselves to what ever they can. If you have the money, install a water softener.
    I have a water softener and an iron filter. I've had them since the tankless was put in.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Where is the unit located? Could it be some local pollutant? Do you regularly use candles or air freshener, or do a lot of baking or laundry nearby? If you can get enough to be visible, stick it in a small glass or jar and add some vinegar and see if it dissolves. While the insides of the heat exchanger might get some mineral deposits (not as much or as quickly with soft water verses untreated), it shouldn't affect the interior. Do you have a humidifier? If so, do you fill it with untreated water?
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6

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    Quote Originally Posted by DaMan View Post
    That white powder is Calcium buildup. All that means is your city water has a hard water, or high mineral count. It is very common. When your tank less water heater heats up the water, the water releases all those hard water compounds and those compounds attach themselves to what ever they can. If you have the money, install a water softener.
    Not from supply water on the fire side of the unit. In most cases when this is happening you have either a venting problem causing condensate in the HX or you have some kind of sustained low fire issue doing the same thing. THe powder is VERY caustic and is ACIDIC as heck. If you ever blow this out DON"T INHALE IT! or you will be very very sorry. Wear a respirator. (Not a dust mask)

    Now what is your vent like? Describe it me. Do you have it on a recirc loop of some kind? Is it doing your heating too though an air handler?

    In a nutshell, if your vent goes up verticaly at all, you should have condensate collector on it to protect the HX. If you are using it as Hydroheat or on a recirc, you need to make sure you do not create a sustained low flow condition as this will cause condensate to form INSIDE the HX and eat it up in just a few years.
    Last edited by Scott D. Plumber; 03-09-2013 at 08:19 AM.

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