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Thread: T&P/Expansion Tank/PRV Issue

  1. #1
    DIY Junior Member b10751's Avatar
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    Default T&P/Expansion Tank/PRV Issue

    New here and have gotten a lot of great info from reading the site. My issue:

    3 years ago, my city installed new meters that had backflow preventers on them. within a week of that, i had some pipes burst due to expanded pressure. Consequently, I called a plumber to have pipe repaired. In addition, i had them install new hot water tank, expansion tank and PRV. Everything was fine until this weekend, when i had some water discharge from the T&P valve on the tank. I 'assumed' that maybe the valve had gone bad, so i replaced it. The very next day, water again discharged from the T&P valve. I put a water pressure gauge on an outside hose bib and it registered around 60psi, but eventually creeped up to around 80. I left the gauge on the bib and checked it later today, and the tattle tale needle had spiked to 160. (my son takes long hot showers) I checked the expansion tank with a tire gauge. 0 psi, and a thump on both ends of the tank sounded like it was full of water. So, this afternoon i replaced the expansion tank. I pre-charged it to 60 psi, and adjusted the PRV til the gauge was reading was 60 on the hose bib. Install went fine, but pressure gauge has now creeped back up to 80. And will drop to about 45 when water is being used, but eventually creeps back up to around 80-90.

    Has the PRV gone bad after only 3 years? Would cleaning the PRV strainer help the situation, or should i just have the PRV replaced? It'll be interesting to see if any water discharges from the T&P after tomorrow.

    I appreciate any info you gurus can provide..

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    PRV needs replacing or rebuilding. Since rebuilding is sometimes iffy, it's usually replaced. That is kind of short for life, but it happens.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member b10751's Avatar
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    Thanks. Is this something a handy diy'er could replace themselves? The defective PRV is a watts 25-AUB-Z3. Lowes sells a comparable watts valve for $75. Do you unscrew the old one and simply screw in the new one? Or would I be better off calling in a licensed plumber?

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    In the Trades Gary Swart's Avatar
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    There are some "ifs" involved here. If the PRV is reasonably easy to get to and work on/around, and if you are able to sweat a solder joint replacing a PRV is not a highly technical job. The PRV that I have is the only one I have installed, but it uses a union on one side and a solid connection on the other. Pipe length can be critical if there is no flex in the pipe, but nothing that careful measuring won't deal with. You should be able to pretty well tell how to install the unit by comparing it to the old one.

  5. #5
    DIY Junior Member b10751's Avatar
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    24 hours and no discharge. Going to hold off replacing the PRV, so hopefully the new expansion tank solved the issue.

  6. #6
    DIY Junior Member b10751's Avatar
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    ok, still no leaking, but the pressure keeps creeping up to almost 90. obviously, the PRV needs replacing. Here is a pic of the current PRV. How do i go about removing it? Do I, first loosen the union nut? Never dealt with union joints before. thanks for your help.
    Name:  valve.jpg
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  7. #7
    DIY Senior Member SteveW's Avatar
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    Yes, loosen the union nut first - and make sure you apply a wrench to the flats on the left side of the PRV when you do so. Once the union is unscrewed, you can turn the PRV off the male fitting on the left (and again make sure you "hold back" with a 2nd wrench to prevent damage to the copper pipe).

  8. #8
    DIY Junior Member b10751's Avatar
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    Thanks Steve.

  9. #9
    Moderator & Master Plumber hj's Avatar
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    In the majority of cases, you will also have to replace the union because they are not a "standard" size.
    Licensed residential and commercial plumber

  10. #10
    In the Trades Gary Swart's Avatar
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    As long as the new PRV is the same length as the old or if there is slack in the pipe(s) this should not be a difficult job. As HJ suggests, the union may not be the same, so you would have to get a new union. I assume the white smears on the screwed connections is pipe dope. Use new dope on the threaded connections, but not on the union.

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