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Thread: New Install (Water Heater) Leaking T & P Valve

  1. #1
    DIY Senior Member molo's Avatar
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    Default New Install (Water Heater) Leaking T & P Valve

    Hello,
    a friend recently had a new Reliance 40g natural gas hot water tank installed and the T&P valve is leaking. The water temp.is not real hot, so I'm assuming it's a pressure issue. They do not have a pressure regulator or expansion tank, but the other homes in the neighborhood don't either and do not have T&P valves leaking.
    What is the reason for this?

    Thanks in Advance
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    You don't need a PRV to have a need for an expansion tank...if the water supply company is replacing their meters, the new ones usually have a check valve in them. Another reason one house may have that issue where another does not is if all of their valves are actually functioning! A toilet valve is often the first valve to leak, and people often don't notice since it just goes down the drain, rather than a faucet dripping into the sink. If all of your faucets and valves are good, and you have a check valve or PRV, you could reach the release pressure on the T&P because there's no relief.
    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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    DIY Senior Member molo's Avatar
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    Quote Originally Posted by jadnashua View Post
    You don't need a PRV to have a need for an expansion tank...if the water supply company is replacing their meters, the new ones usually have a check valve in them. Another reason one house may have that issue where another does not is if all of their valves are actually functioning! A toilet valve is often the first valve to leak, and people often don't notice since it just goes down the drain, rather than a faucet dripping into the sink. If all of your faucets and valves are good, and you have a check valve or PRV, you could reach the release pressure on the T&P because there's no relief.
    Thanks for the reply Jad. I can confirm that the neighboring houses don't have leaking toilets or other fixtures. So is this a bad T&P valve?
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
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    In the trades Dana's Avatar
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    It could be a bad T & P valve, but it's pretty easy to check the static water pressure on the system with a $10 pressure meter on a standard 3/4" hose fitting. The cold side of a laundry hook-up is a good place, but the drain valve on a hot water tank is usually a 3/4" hose fitting too.

    If you have water-hammer issues you can get pressure waves high enough to get a T & P valve to spit a little, more likely if the static pressure is on the high side (> 50 psi).

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    DIY Senior Member Reach4's Avatar
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    http://www.homedepot.com/p/Watts-3-4...IWTG/100175467 is similar, but it records the peak pressure also.

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    DIY Senior Member molo's Avatar
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    The pressure is between 70-80psi, but most houses in the area don't have a problem. And perhaps more importantly the previous water heater didn't either.
    "Any American who is prepared to run for President should automatically, by definition, be disqualified from ever doing so."
    Gore Vidal.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The entire country is moving towards having checkvalves in their clients homes to help protect the rest of the neighborhood. If your water meter was serviced or replaced for some reason, you may have one while the others do not.

    New T&P valves are pretty reliable, but it certainly could be bad. Releasing on high temp (near boiling) would be fairly obvious. You want your test gauge to have a second hand, so you can see what happens over time, rather than a one-time snapshot. Those valves typically open at 150psi. FWIW, a little leak through the toilet fill valve after a WH heating cycle could easily go unnoticed, since it's not a constant thing. A single faucet that drips a little, could relieve enough water to heep the pressure down, too. Again, since it isn't constant, it may not get noticed.

    If your pressure doesn't rise over a 24-hour period, and you know the temp in the tank isn't excessive, change the T&P valve.
    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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