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

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Thomas Gandolfo, May 1, 2020.

  1. Thomas Gandolfo

    Thomas Gandolfo New Member

    Joined:
    Mar 31, 2020
    Location:
    Connecticut
    I had a new pressure regulator installed about a month ago. I have city water. The water pressure regulator is set at 60 psi. Over the last month, it seems to have stayed right around 60 psi. 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 the gauge had shot up to over 100 psi. I ran some water and it finally 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? Would an expansion tank on the HWH resolve this problem?
     
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    A PRV creates a closed system. Heating water expands it that WILL raise pressure until something leaks. The safety valve on the water heater will open at 150-psi, and since the pipes aren't very elastic, they won't balloon much, so any expansion will directly translate into a pressure spike, but it will go back down as soon as you use any water.

    If the PRV that was installed has a bypass valve in it, the expanding water will go back into the supply system, but your pressure will then sit at the supply pressure until you open up a water valve to use some water. Pressure could also be relieved if something leaks in your house. A common item is the toilet fill valve, but even a dripping faucet might be enough, depending on how badly it leaks.

    Anytime you create a closed system, you MUST install an expansion tank if you want your pressure to remain stable. Precharge it to the same setting as your PRV, or 60-psi. THey generally come precharge to about 40, so you'll need a bicycle pump or a small compressor to pump it up. This must be done prior to installation. Once setup and installed, generally, the ET will show the same pressure as your water.

    When the WH runs, that expansion will go into the tank, compressing the bladder and the pressure will rise only a very small amount. WHen you open up a valve, that water will get pushed back out so it doesn't stagnate.
     
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  4. Bannerman

    Bannerman Well-Known Member

    Joined:
    Mar 19, 2014
    Location:
    Ontario, Canada
    A pressure regulator is not a release valve. A regulator valve's function is to regulate a lower pressure downstream from a higher upstream pressure, but in your situation, the higher pressure was created downstream.

    When cold water is heated, it expands. Water can not compress so there needs to be somewhere for that additional water to go.

    Without a regulator valve between your water heater and the city water supply, water expansion would pushback into the city supply, but with a regulator now installed, the regulator will not allow backward flow back to the city supply. With nowhere to expand into, your plumbing pressure will rise until something lets go to release the pressure. Usually, the point of leakage will be the water heater temperature/pressure relief valve, but sometimes, it can be something else such as a weaker hose or pipe fitting.

    You now require an expansion tank to be installed in the cold water line before the water heater.

    Here is a sizing tool to determine the minimum expansion tank needed.
    https://www.amtrol.com/resources-rewards/selection-tools/
     
  5. Thomas Gandolfo

    Thomas Gandolfo New Member

    Joined:
    Mar 31, 2020
    Location:
    Connecticut
    Jadnashua and Bannerman - thank you for your responses. 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 (on the cold water line before the water heater)?

    Is it common to have two expansion tanks (one for the furnace and a separate one for the hot water heater)?

    Thanks again. Really appreciate your help.
     
  6. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Joined:
    Sep 2, 2004
    Occupation:
    Retired Systems engineer for defense industry.
    Location:
    New England
    The expansion tank on the heating system is isolated from your potable water system and yes, you will need a second one on your potable water system to resolve your issue. It generally gets installed on the cold inlet to the WH. Lots of threads here with some pictures if you search.

    Where I live, an ET is required, even if it isn't already a closed system. The Feds have been directing utilities to install check valves on their supplies to prevent the possibility of polluting the water system. Anything that creates a closed system where heating is involved will need an ET.
     
  7. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Yes, and yes.
     
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