Sporadic water pressure increases

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by beachbum64, Apr 19, 2009.

  1. beachbum64

    beachbum64 New Member

    Apr 19, 2009
    Thanks for taking my question. I am experiencing sporadic water pressure increases. The prv is set at 60 psi but, and the time varies, the pressure in the lines will increase to 80 and even 100 psi. I just had the prv replaced one year ago and the pressure has been fine until a couple of weeks ago. I'm beginning to wonder if this may be the result of thermal expansion or is there a way I can test the prv? This problem makes me reluctant to leave the house for fear of busted fittings and/or faucets. Any advice will be appreciated.
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    Do you have an expansion tank before the water heater? If not, add one. If you do, check to see if it is not shot. The tank should be nearly full of air, so if you tap it and it sounds like it's full of water, it's probably shot. If you take the cap off the bottom and check it with a tire pressure gauge, if you get water out, it is shot.

    If you have one, and it doesn't shoot water out, turn the water off to the house, then open a faucet to relieve the pressure, then using the tire pressure gauge, check the pressure in the expansion tank...it should be set to approximately the same as your normal static pressure from the PRV.

    If you have a tank, and it's good, then the prv might have failed. They usually last a lot longer than a year, though.
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  4. SteveW

    SteveW DIY Senior Member

    Feb 11, 2005
    Omaha, NE
    When do you notice those increases?

    Thermal expansion happens when a fairly good "slug" of water is heated by the water heater, tries to expand, but can't back up into the water main due to a check valve or PRV.

    You can test this by running hot water (use a tub faucet to get the fastest flow) for 5 minutes, then watching the pressure as the water heater heats up that replacement water.
  5. Gary Swart

    Gary Swart In the Trades

    Sep 1, 2004
    Yakima WA
    What can happen is the pressure can get high enough to trip the T/P valve on the tank. Sometimes the T/P will reset when the pressure drops, but sometime it won't. If there is no place for the water to drain, you can have a real mess. A thermal expansion tank prevents all of this as long as the tank is working right.
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