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Thread: T&P Valve failure???

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  1. #1
    DIY Member dirtmover's Avatar
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    Default T&P Valve failure???

    I shut my water heater down for two weeks while on vacation. I turned the heater back on this afternoon and after running for about an hour the T&P valve opened up discharging water over the basement floor. Is this a common failure mode for this type of valve after the heater has been allowed to cool down? I've replaced the valve and am watching closely as it heats up again.


    T&P Valve looking at two sides.
    Last edited by Terry; 08-18-2009 at 11:05 AM.

  2. #2
    DIY Senior Member SteveW's Avatar
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    Could be a bad T/P valve -

    or could be thermal expansion!

    Do you have a pressure reducing valve? If so, do you have an expansion tank?

  3. #3
    DIY Member dirtmover's Avatar
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    I am on a well so, assuming there is not a check valve in the tank(?), the pressure tank should act as an expansion vessel - correct? The pressure was not high according to the gauge and the temperature did not seem excessive.

    BTW, it seems fine now with the new valve. I'm just curious if it's common for them to fail after allowing the tank to cool and sit unused for a few days.

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
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    In normal operation, you don't start your WH with all cold water. Because you did, you ended up with a lot more expansion than you normally would. That unusual volume might have given you problems with your bladder tank if the static pressure in it is low. Try shutting off the pump, opening a valve until the water stops flowing, then check the pressure in your tank. It should be 1-2# less than the turn-on pressure.

    Or, your old valve could have worn out.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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