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Thread: T&P dripping & pressure low

  1. #1
    DIY Junior Member ChrisRice's Avatar
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    Default T&P dripping & pressure low

    Okay this is driving me crazy. I'm calling a plumber Monday but wanted to see if anyone had any thoughts just because I'm trying to figure out whats wrong. This may be a windy post, so bear with me

    So last weekend I took a shower and noticed that the initial pressure was pretty high then lowered. I've had some pressure issues in the past so I started investigating.

    So the past pressure issues caused me to install a PRV and an expansion tank. Pressure set to ~58. Seemed to have solved everything. This was about 6 months ago.

    After shower incident last week, I hooked the pressure gauge up to the faucet and pressure is 58, two days go by where I'm noticing when I turn the hot water on there's a burst of pressure and back to normal (water kind of spurts like when there's air in the line).

    Sounds like thermal expansion to me (thanks to reading all your all's posts on here!). So I check the expansion tank. Hollow ping on one side, metal thud on the other like it's supposed to be, check the pressure it's right around 58. Seems like it's working properly, no?

    Then I check the T&P valve. It seems okay as well. Noticed the temp was set to "B" which I don't remember setting it to and neither does the wife, but the water had been pretty darned hot, so I turned it back down to "A."

    Checking the next morning, a small amount maybe 2-3 tablespoons of water has come out of the T&P drain tube.

    Go check pressure again, it's 48 which is where it's remained for the last two days. This morning I did have the sputtering again out of the faucet when I first turned on the hot water. And still getting small amounts of water from the T&P. Pressure still at ~48

    I'm thinking the testing the T&P got it stuck open? Would this cause the pressure to drop? I'm bewildered by this entire process....any thoughts? Water heater is from '02, not sure if it's ever been drained or anything (I haven't done it since we've lived here).

    Thanks!

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Sometimes a T&P can age (spring weakens) , or get dirt on the seal, allowing water to drip past.
    I would consider replacing the T&P, an inexpensive part and see what happens.

  3. #3
    DIY Junior Member ChrisRice's Avatar
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    Thanks, that was the plan, though I'll have a plumber do it just to talk about some other things as well.

    So would the leaky t&p cause the pressure to drop? That's the part that seems odd to me, I didn't adjust the prv and im close to 10 psi lower than yesterday. Low pressure makes me feel better than high pressure but it just seems odd.

  4. #4
    Forum Admin, Expert Plumber Terry's Avatar
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    Any leak will prevent pressure build up. This could be the T&P or even a leaking toilet flapper.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Note, unless you turned the water off and opened a faucet, the expansion tank will just read the supply pressure. You need to check its static pressure without applied water pressure. It should be about the normal water pressure (they come precharged to about 40#, which is too low for your situation). WHen it is in the closed circuit, the air pressure will EQUAL the water pressure, unless you precharged it to a value above the water pressure.
    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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