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Thread: Faulty pressure regulating valve?

  1. #1

    Default Faulty pressure regulating valve?

    Hey all. I have a pressure guage on the supply line to my hot water heater. It is registering a static water pressure of 120 psi, but when I open a valve, it drops to 45 psi. I read that a dropoff of 3-12 psi is normal with the Honeywell Braukmann D05 which I have, but this swing of almost 80 psi seems steep. I am worried that over time the pipes will fatigue. Does anyone know if this sounds like a problem with the pressure regulating valve? Thanks for any advice.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Install an expansion tank...sounds like you have either a pressure reduction valve or a check valve. You use hot water, replacing it with cold. Then you turn the tap off. The heater heats the water which gets bigger in volume - the pressure goes up until you open a faucet to run water again. Classic example of the need for an expansion tank...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default prv

    You have to determine whether the pressure is rising immediately after flow stops, or possibly over a period of time even when the burner is off, in which case it is a faulty PRV. If the pressure only increases when the burner is operating, then it is thermal expansion and you need an expansion tank. Whey is the PRV only on the hot water side? That can create problems in the shower valves.

  4. #4

    Default PRV response

    Thanks for the responses. It is definately not thermal expansion. The pressure goes up quickly, and maxes out within a minute.
    AJ, actually, the prv is on the main supply line. I only have a guage on the line into the hot water tank.
    I haven't tried to adjust the prv. Should I give it a shot in case the previous owner had it wide open, or to see if it frees something up?

  5. #5
    DIY Member Vitaliy's Avatar
    Join Date
    Sep 2005


    The right place for the PVR is where main supply line entered

    the house right after main shutoff valve and before or after

    water meter. Looks like yours in a right place.

    Do you have an expansion tank?

    If you don’t have one you should install it immediately. You

    have a PVR and if this PVR does not have a bypass feature

    your system is a “closed system”. Each “closed system” with

    water heater MUST have an expansion tank. Actually pressure

    may go up very quickly if water heater is running. So, buy

    saying “It is definitely not a thermal expansion problem” make

    sure you do have an expansion tank and if you don’t have one

    your water heater was not running during your experiment

    with rising pressure. One more detail to mention. If you have

    an expansion tank make sure it is not water filled (it may have

    broken bladder or diaphragm).

    If there are no any check valves somewhere installed on your

    plumbing system static pressure (no water use/flow) should be

    the same on cold and hot water lines.

    - Vitaliy (not a plumber)

  6. #6
    Plumber jimbo's Avatar
    Join Date
    Aug 2004
    San Diego


    Your symptoms are classic for a faulty regulator. It has a leak in the diagphragm, allowing street pressure to build up in the house. At the same time, the regulating function is defective, causing pressure drop under load.


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