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Why does my house water pressure rise higher than the regulator setting

TomGan
TomGan Member Posts: 15
I had a new pressure regulator installed about a month ago. I have city water. The water pressure regulator is set at 60psi. Over the last month, it seems to have stayed right around 60psi. However, this morning I noticed the pressure relief valve on my new water heater started to leak. I do not have an expansion tank on the hot water heater (HW heater is only one month old). I checked the regulator on the water line and it had it shot up to over 100psi. I ran some water and it came back down and now is at 60 again.

Why would the water pressure be so much higher then the release valve setting? Is this common. Shouldn't the valve protect against a surge? Is this why the PRV leaked on the HWH?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 15,700
    If you have any device which is, or acts like, a check valve (like your pressure reducing valve), you MUST have an expansion tank on the system or at least on the hot water.

    As water is heated, it expands -- or tries to. If there is no expansion tank, it takes it out as a pressure increase. Elementary physics. Fortunately, your pressure relief valve on the water heater operated -- otherwise you would have blown a pipe joint somewhere... or the water heater tank... or something else soggy.

    It's not just common, it's inevitable -- and whoever put the pressure reducing valve on your system should have put an expansion tank on at the same time.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    ZmanHomerJSmithkcopp
  • TomGan
    TomGan Member Posts: 15
    Jamie, thank you. I should mention that I have an expansion tank on my oil furnace that heats the water heater. Should I also have an additional expansion tank on the water heater?
  • Jamie Hall
    Jamie Hall Member Posts: 15,700
    Yes, as I mentioned to you in my PM to you.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 4,907
    TomGan said:

    Jamie, thank you. I should mention that I have an expansion tank on my oil furnace that heats the water heater. Should I also have an additional expansion tank on the water heater?

    Yes but it needs to be one designed for potable water, and it's charge needs to match your incoming water pressure. Charged needs to be checked initially before installation, and afterwards by isolating the expansion tank with zero water pressure affecting the reading.
    steve
    HVACNUT
  • HVACNUT
    HVACNUT Member Posts: 3,904
    edited May 2020
    No not on the water heater. On the domestic cold side, preferably near the water main.
    Charge the tank to 60 psi to match cold water pressure.
  • jumper
    jumper Member Posts: 1,609
    Remember shock arresters that were just dead end vertical branches? Are they recharged when you drain water from the house? Should they be aligned a little off vertical?
  • HomerJSmith
    HomerJSmith Member Posts: 1,270
    edited May 2020
    What model and make of pressure regulating valve? Street pressure regulating valves usually have a bypass that allows higher pressure in the house because of the expansion of hot water to flow back to the street main. Does the PRV have a pressure gauge on it? Some jurisdictions require a reduced pressure backflow preventer, I think, in which case you need a potable expansion tank on the house water.

    60 psi set pressure run up to 100 psi would indicate to me that the PRV is not regulating and may be faulty or incorrectly adjusted or needs an expansion tank.

    The pressure relief valve on the water heater should hold 100psi. You obviously don't have a check valve on the cold water supply to the W/H. If you did you would already have expansion tank on the W/H.

    How fast does the rise to 100 psi in house pressure occur after you turn on a cold water valve to bring the pressure down to 60 psi? At night before you go to bed you can shut off the cold water supply to the W/H turn the heat knob to vacation and open a cold water valve to bring the house pressure to 60 psi and then see what the pressure is in the morning. If it is still 60 psi then the Pressure Regulating Valve is probably ok. Turning on the cold water supply to the W/H and turning up the dial to where it was before and if the pressure rises, then the culprit is the water heater.
  • dopey27177
    dopey27177 Member Posts: 440
    Two things can be going on here.
    1. Dirt in the domestic water supply (like rust or possibly cement from a cement lined municipal water main system) lodges under the seat o the prv. to correct that condition install a strainer before the the prv.
    2. The hot water heater, when you heat water in a confined space the water tries to expand. As it tries to expand there is no room for the water to increase in volume, that causes the increase in pressure. If the prv is good it will remain in the closed position and act like a check valve. And the pressure in your water pipe increases.


    Jake
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