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Thread: Water heater question - cold water, water leaking thru overflow pipe

  1. #1
    DIY Junior Member
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    Default Water heater question - cold water, water leaking thru overflow pipe

    Hope to get some insights before calling professional.

    Issues:
    Cold water.
    If temp is set high, gas burner is ON.
    After few minutes, water will start to leak out of overflow pipes.
    Water coming out of overflow pipe is warm.
    After few minutes of shutting off the burner (by turing the temp setting to low), water stops leaking from the overflow pipe.

    When draining the water thru the drain valve, water flow is not uniform with lots of calcium carbonate (?).

    I am wondering if I should attemp to replace T&P valve or Thermocouple.
    Or start looking at a new gas water heater.


    Any advise will be most appreciated.


    Thanks

  2. #2
    In the Trades Gary Swart's Avatar
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    Do you have a pressure regulator valve? It sounds to me like you have one but do not have a thermal expansion tank. Briefly what happens is when water heats it expands. In a water system without a pressure regulator, the expansion is absorbed by the city water main, but a pressure regulator has a check valve that prevents this from happening. The expansion has to go somewhere, so if there is no thermal expansion tank, the TP does its job when the pressure gets to 150 psi and release some water and relieves the excess pressure. If you have a thermal expansion tank, it may be shot. Some newer water meters have a check valve in them also, so even without a PRV you could have the same problem.

  3. #3
    Master Plumber nhmaster's Avatar
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    yep, do a quick pressure test with the unit cold and then hot and see if the pressure rise exceeds the valve setting. If it checks out then check to see if the tank temp exceeds the T&P valve's rating. If everything is good, change the T&P valve. the tank thermostat should be set at 120 normally

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Default T&p

    If the valve leaks only while the burner is operating, it is a pressure build up problem. If it were leaking because of temperature, it would not stop until enough water is released to lower the tank's temperature. Changing the water heater OR the valve will not cure the problem. You have to determine why it is happening and correct that.

  5. #5
    DIY Junior Member
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    Thanks for the advise.


    It is gas water heater: A.O. Smith FGR-40-242 model.
    It was working fine until I replaced the burner thermocouple few months back.
    (pilot light won't stay on)

    I have T&P valve, and if I pull the lever, water comes out from the overflow pipe.

    I do not believe I have thermal expansion tank. ( or it it inside the water heater?)

    When burner is ON, the water coming out from overflow pipe is barely warm.
    (water starts leaking out less than 10 minutes of burner ON)

    I am leanning toward the T&P valve. Is T&P valve uniquie to each ewater heater make?


    Agan, Thanks for all the information/advise.

  6. #6
    Moderator & Master Plumber hj's Avatar
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    Default T&p

    They are generic, but your description implies that it is working correctly, and the problem is a thermal expansion pressure increase. If so it will only be corrected by installing an expansion tank, and no they are not inside the water heater. IF you had one, you would have asked us, "What is the white, (or blue), tank connected to my water heater's pipe?"

  7. #7
    DIY Senior Member Runs with bison's Avatar
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    jonyi,

    Get a $10 test gauge and connect it (typically to a hose connector, valve open.) You really don't know what is happening without it. The gauge will indicate the max pressure it sees (red needle) and show the current pressure with the black needle. You also need to determine if you do or don't have PRV or expansion tank. If all you have is a valve coming into the home with no unexplained devices/fittings in the line between the meter and the tank then you lack these features. I'm assuming you aren't on a well.

    You should be able to read the water temperature set point from the gas thermostat. It has hash marks in 5 degree increments as memory serves. What temp are you setting it to?

    Sounds like you could have one or a combination of the following:
    1. Don't have a PRV and need one.
    2. Have a PRV that has failed or is set too high.
    3. Need a thermal expansion tank.

    I get about 20-25 psi rise without a thermal expansion tank in my home. I intend to install one when I replace the PRV.

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