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Thread: T&P valve on Tankless Heater

  1. #1
    DIY Junior Member loaderman's Avatar
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    Mar 2012

    Default T&P valve on Tankless Heater

    I have a Tankless heater, ever since I bought the house 1.5 years ago the T&P valve has been discharging slightly when you turn off a hot water tap. I was told this is normal. Is it?

    Now the T&P valve is leaking constant when you use hot water. The water temperature is not overly hot coming out of the relief vlave, I can hold my hand in a pail of it for a minute or so. Wanted to take a temperature on it but do not have a thermometer.

    The tank was at 50C and I turned it down to 40C and it leaks a lot less water but still does leak a little.

    We also had a power outage if that makes any difference, although we were on holidays, however 4 showers were taken and 3 loads of laundry done before it started to leak after we got back.

    Figuring I'll probably just change the T&P relief valve and see if that does it.
    Any other thoughts or ideas?

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    I would change the T&P
    Sometimes they get something inside that prevents sealing.

    Last edited by Terry; 03-30-2012 at 10:56 AM.

  3. #3


    do you know the temp & press setting of the valve? is there any check valves in the system? it seems like it's narrowed down to a pressure issue. not overheating.

  4. #4
    DIY Junior Member loaderman's Avatar
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    Mar 2012


    Old pressure relief was 201f and 150psi(?) just going from memory, replaced it with the same and seems to be fine now.


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