Puzzled over this TECV valve issue

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by zaldwaik, Aug 21, 2013.

  1. zaldwaik

    zaldwaik New Member

    Messages:
    4
    Location:
    Virginia
    I have a water heater which has a pressure relief valve, and a Thermal Expansion Control Valve (TECV). The TECV sets on the incoming cold water line just before the water heater and cold line is connected directly to water main.

    Last month the TECV started to release water through the small attached pipe continuously. I hired a plumber who said you need a new TECV valve. It was hard to find but I managed to purchase one. He removed the old valve and put in the new one. It worked fine until this morning when it started releasing water again.

    At this point neither I nor the plumber know what to do. I do not think the new TECV is defective (or the old one). The main water pressure is 70 PSI as it has a pressure reduction valve. Could this be a bad water heater?

    The pressure relief valve (150 PSI) on the water heater itself appears to work fine. It releases water when tested. It is a higher threshold than the TECV (80 PSI). The water heater is 13 years old and it is Rheem.

    Turning hot water on for a couple of minutes stops TECV from releasing water until the pressure builds again.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    The generally accepted fix for this is an expansion tank, not a TECV. Plain fact, water expands when it is heated. Depending on the system, it can either start to blow up softer hoses like balloons, leak out of the weakest valve, or if your house isn't a closed system, push water back to the water main. More and more water supply companies are installing check valves, which makes your house into a closed system. So, has the water company changed anything recently? Do you have a PRV? What is your static water pressure? How did you test the WH T&P valve to get 150psi? No domestic water system should ever have more than 80psi, and if it does, needs regulation. So, there may be more than one thing going on. But, first, I'd probably buy a water pressure gauge and actually check what you have. Pick one up with a second, 'tattle tale' hand and leave it connected for say 24-hours to measure the peak pressure.

    Since most things in your water distribution system cannot expand much, when the water does, it can raise the pressure radically...it doesn't take much expansion. It also doesn't take much to relieve that pressure - a leak somewhere, either intentional or by defect. Better to allow it to expand into the expansion tank, maintaining your set pressure and not stress things.
  3. hj

    hj Moderator & Master Plumber Staff Member

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    IT sounds like your TECV is doing what it is supposed to do, namely, release pressure created by expansion, since it usually just a pressure relief valve set at a lower pressure than the 150 psi of the heaters relief valve. The only way to "absorb" expansion is with a properly installed and initialized expansion tank.

    http://www.apollovalves.com/_products/78LF-RV/EXV LF SS1177.pdf
    Last edited by a moderator: Aug 22, 2013
  4. zaldwaik

    zaldwaik New Member

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    4
    Location:
    Virginia
    Thanks both for the quick response. See answers to your questions.

    If TECV is releasing water all the time, would the expansion tank gets filled up quickly? I guess I am assuming releasing some water would reduce pressure until it builds up again. But that is not happening with the valve, and I am not how the tank would solve it. Thanks
  5. Terry

    Terry Administrator Staff Member

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  6. hj

    hj Moderator & Master Plumber Staff Member

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    Location:
    Cave Creek, Arizona
    The air "bubble" gets smaller when the pressure increases then goes back to its original size when a faucet is opened and the tank reverts to its static pressure. Your valve release water and when the water cools and "shrinks" new water replaces it, then if the burner comes on again, it has to evacuate that new water again, which is why he "leaking water" cycles.
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    There are VERY few situations where a TECV is ever called for. Convention and code calls for an expansion tank when you have a closed system. A plumber that doesn't understand that isn't much of a plumber. In fact, without one on your system, it would indicate a problem if it DIDN'T expel water during the WH reheat cycling.
  8. zaldwaik

    zaldwaik New Member

    Messages:
    4
    Location:
    Virginia
    Thanks, that is what two plumbers told me so far. They have not seen this before. What would be the risk if I take it out from the picture and simply rely on the pressure relief valve?
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,149
    Location:
    New England
    Good practice (and code many places) requires an expansion tank when you have a closed system...it isn't expensive to install one...just do it! The T&P valve on the WH is an emergency, safety device. It likely will open and release some water on a regular basis, and it might gunk up, then not open should it need to. This is not to be taken lightly - if the tank has a problem, and the valve needs to open, it can literally blow out through the roof.

    Bottom line, water expands when it is heated, pipes don't, as a result, the pressure will go up until something gives. This could be the supply hose to your washing machine, the refrigerator ice maker, a faucet, a toilet, etc. You do NOT want to be continually stressing these things, and that is exactly why you need an expansion tank. You paid to keep the pressure down with a PRV...why would you then allow it to get high every time the WH runs?
  10. Gary Swart

    Gary Swart In the Trades

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    I can virtually guarantee you that if your new PRV does not have a bypass feature for expansion, your T/P valve will release at least a cup and probably more water every time the water heater heats water. Sometimes a T/P does not close tightly after the pressure drops, so if that happens, the leak will be constant. An expansion tank installs with a tee in the incoming water pipe. There is a fitting that comes with the tank that connects the tank to that fitting. The tank must be securely supported, but other than than it is a very simple installation.
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,149
    Location:
    New England
    If a PRV has a bypass (by no means to all of them), the internal house's water pressure will rise to that of the supply side before it can allow water back through to the supply side (and often, it has to get slightly higher). Again, why put in a PRV and then live with the pressure spiking every time the WH reheats a quantity of cold water? Put in an expansion tank, and be done with it! For maybe $50 in parts, it's fixed. The tanks do eventually fail, but then it's simply spin the old one off, preset the pressure on the new one, and spin it on.
  12. zaldwaik

    zaldwaik New Member

    Messages:
    4
    Location:
    Virginia
    Thanks to all who responded. I have another twist on this situation as I was going to install the expansion tank. It seems as though the PRV is failing to reduce pressure somehow. My previous readings were wrong. The pressure measures 90 PSI from garden spigot. I changed the setting on the PRV down and the pressure does not change (TECV continues to release water). However, once I turn the water on from one of the faucets I see the pressure is actually down by observation (water is slow) after first 2 seconds and the gauge goes down to like 20 PSI (TECV stops). Once I turn the faucet off, the pressure builds up again and goes back to 90 PSI which also causes the TECV to start releasing water. I bought a new gauge thinking mine was defective, but it showed the same numbers.

    It seems the PRV is only working when the water is on, is my PRV failing?
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,149
    Location:
    New England
    One sign of a PRV failing is its inability to hold the pressure steady. While you can buy rebuild kits, the kits cost almost as much as a whole new thing, then you have the risk of messing up a seal, doing it wrong, and the time involved...sounds like it's time for a new PRV. Set the precharge to the expansion tank to a pound or two less than your PRV setting - this puts the bladder at its 'static' point and gives it the largest possible useful volume without overstretching it. That must be done with no pressure on the water side, so it's easiest to do before installation. If you check the air pressure after turning on the water, the air pressure will always equal the water pressure, and not tell you the precharged value.
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