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Thread: Leaking T&P Valve

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  1. #1
    DIY Junior Member ScrewedByNCGC's Avatar
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    Default Leaking T&P Valve

    I've got a 50 gallon low-boy that has been leaking for about 3 years. It's a Bradford-White or AO Sloan, not sure which. I never exactly knew where because it was so slow but in the past 6 months it got to the point where I could see an occasional drip from the temp & pressure valve drain pipe. I put a bucket there and it fills up with about 8 oz. of water in three weeks; it's enough to keep that area of the crawl space moist and moldy.

    As an experiment I adjusted the water pressure regulator valve by turning it three turns CCW. The valve has a plastic collar on the adjustment nut to keep it set at a preset point (see the attached pic). The valve body reads, "5 - 65 PSI" so I presume the setting is something like 45 because the water flow before adjusting was actually kind of weak; now, it's so weak the shower thing won't engage unless I hold it for a long time. Anyway, I turned down the pressure, set the bucket and a month later no water coming from the T&P valve.

    My water heater was repaired (if you can call it that) in 2008, which was near the end of its warranty period but still within it. Long story short, only parts were covered under the warranty ($29) but the labour was not ($135). I bring this up only because this incredibly slow drip coincidentally started about the same time my hero showed up and performed his 8 minute miracle repair.

    I've read from the experienced users that 80 psi is the max a household should have -- I am quite certain I am well below that. To give you an even better idea how low it already is, when I hook up one of those oscillating sprinklers it sticks in one position because there ain't enough pressure to keep it moving.

    So, that leaves temperature. I have never adjusted the thermostat on the low boy but I did check out the setting once repairs were made and it was and still is set to the exact middle of the dial. I don't know the exact water temp coming out but if you turn on the hot tap all the way you can keep your hand there and it won't get burned (but it is warm enough).

    Appreciate any comments.
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    Last edited by ScrewedByNCGC; 07-13-2011 at 05:17 PM.

  2. #2

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    So the tank is at least 9 years old.
    If the T&P has not been replaced, it could have aged. Springs can lose their mightiness.

    If you have such low flow that the tub diverter and the sprinklers are giving you grief, then you may need a rebuild or replacement of the PRV.
    They can go bad over time.
    If your PRV doesn't have a pressure bypass, then you might think about an expansion tank.
    I would look first at the T&P though.

    Any tank that gives you ten years, had pretty much given it's all.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    If the T&P has weeped for years, it could be worn out. But, as also mentioned above, (and I take exception to the bypass negating the need of an expansion tank) you probably either don't have, or have an inoperative expansion tank. Depending on how much hot water you draw off, and the temperature you have it set, and how cold the incoming water is, will determine how much that water expands when it gets heated. It will leak out the weakest point, and that may be the T&P valve if the rest of the system is tight.

    A PRV with a bypass will not open until the house pressure gets above the supply pressure which sort of negates the benefit of stable pressure with no peaks. Depending on how high the supply pressure is and how well the bypass and the rest of the PRV is working, the house pressure can momentarily get high enough to cause the T&P to open. Since water doesn't compress, a little expansion can create a lot of pressure increase - easily enough to cause the T&P to open to relieve it.

    The magic test for this is a pressure gauge. You can pick one up at a big box or hardware or plumbing store for in the order of $10. Get one with a tattle tale hand...this will show the peak pressure. Leave it hooked up for at least 24-hours and check both the static and peak pressure. It will help you to also adjust the PRV to a reasonable pressure (normally somewhere around 50# is a good value).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    In the Trades Jerome2877's Avatar
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    It looks like you have an expansion tank already, its probably failed and that is more than likely the problem. I would still do the pressure checks though to make sure the prv is still working. It would be a good idea to change out the T&P valve as well. If doing this yourself use a bicycle pump to increase the air pressure in the new tank to your static water pressure.

  5. #5
    In the Trades Gary Swart's Avatar
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    If the expansion tank has failed, it will be full of water. Tap on it and you should be able to tell if it is waterlogged by the sound. If it needs replacing, be careful when removing it as it will be fairly heavy. You will need a pressure gauge to adjust the PRV and expansion tank settings. They should be equal. Use a small hand air pump on the expansion tank. It's very easy to over inflate the tank because the volume of air needs is quite small and a big air compressor puts out too much air very quickly and that will easily rupture the bladder in the tank. It is possible the T/P needs replacing, but check the tank first.

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    Another quick verification of a failed expansion tank is that you'll get some water out when you try to test the air pressure, but being full of water is usually a big red flag. If the air valve is leaky, it's possible it just needs some air to recharge it. Note, though, that you can only check the air pressure when there's no water pressure on the other side, otherwise, the air pressure will be the same as the water pressure. So, to test and set the pressure in the expansion tank, you need to shut the water off, open a valve (any faucet will do) until there's no pressure, then measure the air pressure in the tank.
    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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