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Thread: Dripping thermal expansion relief value

  1. #16
    DIY Senior Member Reach4's Avatar
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    My confusion was that I thought it was proposed to get rid of the relief valve: http://www.watts.com/pages/_products...d=64&parCat=85

    I see now what nobody was suggesting to remove the safety relief valve on the top of the water heater.

  2. #17
    Retired Defense Industry Engineer jadnashua's Avatar
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    The T&P on the WH is required...it opens at MUCH higher temperatures and pressures to ensure the WH doesn't rupture. A steam explosion can literally flatten a house...you want it to work! A residential system, by code most places, says you need a pressure-reduction valve if your water exceeds 80psi. No idea what your pressure relief valve is set to, but it must be higher than your nominal max pressure, or you'll be wasting water all of the time to relieve it. Without an expansion tank, that relief valve is keeping your pressure down. A PRV may have an internal bypass, but it can only open when the house pressure exceeds the incoming water pressure - this means your pressure is not stable, and higher than code. Not all PRV's have bypass valves, either.

    You do not need that relief valve. When the PRV starts to malfunction, it could help, but by then, it may no longer work. It could be left in, but they usually are more trouble than they are worth. The expansion tank just provides a place for that expanding water to go. Because it is compressing air, the amount of pressure rise is small for the volume of water needed, and your overall pressure will be pretty stable as long as the PRV is working and the ET is not waterlogged.
    Jim DeBruycker
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  3. #18
    Forum Admin, Expert Plumber Terry's Avatar
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    I see now what nobody was suggesting to remove the safety relief valve on the top of the water heater.
    The T&P Valve?
    Not unless you want that water heater to launch itself through the roof and land on your neighbors home.
    Last edited by Terry; 10-23-2013 at 02:50 PM.

  4. #19
    In the Trades Gary Swart's Avatar
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    Jerome, you're still mixing terms. Every water heater come equipment with a temperature/pressure safety valve, commonly referred to as a T/P valve. It will trip if the temperate or pressure reaches the danger points. Water heaters can and do explode, and I mean big time explode if this valve does not open. If your incoming water pressure is excessive, that's 80 psi or more, you need a pressure regulating valve, commonly called PRV. This will lower the pressure to a safe level. The PRV does have a slight downside. Most of them contain a back flow feature. I'll come back to that feature in a minute. We all know that heated water expands and it does not compress. This means when you water heater starts to heat, temperature builds up quite rapidly. If you do not have a PRV, the expansion can be absorbed by the city water main and you have no problem. However, with the PRV, the expansion has to find somewhere to go, and the back flow feature prevents it from get to the city main. It might find a weak toilet valve, but often it will trip the T/P safety valve. The cure for this is with a Thermal Expansion Tank that is installed in the incoming cold water line between the PRV and water heater. This tank provides a temporary escape route for the expansion. It is air charged to match the PRV setting. Hope this clears things a bit for you.

  5. #20
    Retired Defense Industry Engineer jadnashua's Avatar
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    That extra pressure relief valve that was leaking was an indication that the house pressure was too high OR there was no accommodation for expansion when the WH ran. Once you have an expansion tank in there, you do not need that relief valve (do NOT confuse this with the T&P valve on the WH - that MUST stay). Most people find that the pressure relief valves tend to start leaking as they age, even if the pressure isn't too high, so they're kind of a nuisance. You CAN keep it if you want, and it would be another level of protection. The vast majority of houses do not have one, and work just fine. FWIW, the T&P valve can also start to leak as it ages, especially if you have hard water and it gets tripped because of no expansion tank. You should test the thing annually, but as it ages, that may cause it to not seal after the test. One way to look at that, is it probably should have been changed anyways. Sometimes, the tank fails before the valve does.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #21
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    Quote Originally Posted by jerome2877 View Post
    that is a thermal expansion relief valve and is in place of an expansion tank, so absolutely remove it if you install the tank. It is doing the job it was designed for but it is a waste of water.
    you are all missing the point !
    This is the correct answer that is a ball valve to shut the water off and a combination thermal expansion relief valve that opens at 80 psi
    to relief excess water pressure and yes it is doing exactly what it is designed for ! ! And it also wastes water !

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  7. #22
    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by MACPLUMB 777 View Post
    you are all missing the point !
    This is the correct answer that is a ball valve to shut the water off and a combination thermal expansion relief valve that opens at 80 psi
    to relief excess water pressure and yes it is doing exactly what it is designed for ! ! And it also wastes water !
    No, I don't think we all are missing the point...this was already discussed. But, the better solution is an expansion tank - and maybe a PRV, if the supply pressure is also high, then the thing, if you left it there, should never open except if the other things fail.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #23
    In the Trades Jerome2877's Avatar
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    Quote Originally Posted by Gary Swart View Post
    Jerome, you're still mixing terms. Every water heater come equipment with a temperature/pressure safety valve, commonly referred to as a T/P valve. It will trip if the temperate or pressure reaches the danger points. Water heaters can and do explode, and I mean big time explode if this valve does not open. If your incoming water pressure is excessive, that's 80 psi or more, you need a pressure regulating valve, commonly called PRV. This will lower the pressure to a safe level. The PRV does have a slight downside. Most of them contain a back flow feature. I'll come back to that feature in a minute. We all know that heated water expands and it does not compress. This means when you water heater starts to heat, temperature builds up quite rapidly. If you do not have a PRV, the expansion can be absorbed by the city water main and you have no problem. However, with the PRV, the expansion has to find somewhere to go, and the back flow feature prevents it from get to the city main. It might find a weak toilet valve, but often it will trip the T/P safety valve. The cure for this is with a Thermal Expansion Tank that is installed in the incoming cold water line between the PRV and water heater. This tank provides a temporary escape route for the expansion. It is air charged to match the PRV setting. Hope this clears things a bit for you.
    Thanks Gary but I think your the one that needs things cleared up. Like I said the valve is designed for thermal expansion relief and instead of a bladder tank it just drains off to accomplish this. While I agree that an expansion tank is a better solution, the valve (like Macplumb agreed) is doing its job!

  9. #24
    In the Trades Jerome2877's Avatar
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    Quote Originally Posted by jadnashua View Post
    That extra pressure relief valve that was leaking was an indication that the house pressure was too high OR there was no accommodation for expansion when the WH ran. Once you have an expansion tank in there, you do not need that relief valve (do NOT confuse this with the T&P valve on the WH - that MUST stay). Most people find that the pressure relief valves tend to start leaking as they age, even if the pressure isn't too high, so they're kind of a nuisance. You CAN keep it if you want, and it would be another level of protection. The vast majority of houses do not have one, and work just fine. FWIW, the T&P valve can also start to leak as it ages, especially if you have hard water and it gets tripped because of no expansion tank. You should test the thing annually, but as it ages, that may cause it to not seal after the test. One way to look at that, is it probably should have been changed anyways. Sometimes, the tank fails before the valve does.
    Nope, the point your missing is the fact that thermal expansion accommodation was provided and the leaking valve you say starts to leak with age is designed to leak and is doing its job.

  10. #25
    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by Jerome2877 View Post
    Nope, the point your missing is the fact that thermal expansion accommodation was provided and the leaking valve you say starts to leak with age is designed to leak and is doing its job.
    You seem to have missed the "even if the pressure isn't too high" bit.

  11. #26
    In the Trades Jerome2877's Avatar
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    Quote Originally Posted by Reach4 View Post
    You seem to have missed the "even if the pressure isn't too high" bit.

    No, he was stating that the leaking valve was "an indication that the house pressure was too high OR there was no accommodation for expansion". I am saying that in fact that valve is the "accommodation for expansion"

    The valve like anything mechanical could fail and start to leak when its not supposed to but I don't see where I am missing anything here?

  12. #27
    In the Trades Gary Swart's Avatar
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    In my opinion, you had Rube Goldberg do the plumbing.

  13. #28
    Jack of all trades DonL's Avatar
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    Most of the safety valves I have played with are not made for Cyclic operation. Some do not even auto-reset.

    You can build a old school expansion / hammer Protector - Tester with a dead ended piece of pipe.


    A Expansion tank is the best solution, If the problem is do to heating water.
    Last edited by DonL; 10-24-2013 at 06:26 AM.
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  14. #29
    DIY Junior Member psyq's Avatar
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    Home Depot was actual sold out on all their pressure gauges. I'll see if I can find one today somewhere else.

    I did consider a DIY gauge from assorted fittings... but, nah

  15. #30
    In the Trades Jerome2877's Avatar
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    Quote Originally Posted by Gary Swart View Post
    In my opinion, you had Rube Goldberg do the plumbing.
    You find this valve that complex? lol

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