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Boiler water pressure

lrodptl Member Posts: 10
My boiler pressure is always around 30-35 PSI. I have bled water off but it recovers back to 30-35 within seconds. Help,please.


  • DZoro
    DZoro Member Posts: 1,048
    Picture of your system would help. Possible your pressure reducer is dirty and not closing. Setting may have been changed? By pass not closing if you have one. A few other things too, but start there.
  • Jamie Hall
    Jamie Hall Member Posts: 21,110
    First off, if your pressure relief valve isn't opening to drain that pressure off, kindly turn off the boiler with the power switch so that it can't possibly run. Do that now, before you read the rest of this...

    OK, so you are back with the switch off? Good.

    Next item is to find out what the problem is. Does this boiler also heat domestic hot water? If so, there may be a leak from the domestic hot water side into the boiler. Shut off the domestic hot water and open a hot water faucet somewhere. You should get no flow (if you do, there's a cross connection between hot and cold, which is another problem).

    Now shut off the water from your water system to the boiler itself. Drain the boiler down to 15 psi. Does it stay there? If so, your pressure reducing valve may be stuck open, or partly open -- if so, it will need replacing. If it stays there for some time, good -- try turning the water to the boiler back on. It should still stay there; if it starts to go up again, that's another sign that the reducing valve is faulty (or if there is a bypass valve, that that is leaking).

    So... is the boiler sitting at 15 psi? Now turn it back on and let it start to heat up. If the pressure rises much above 18 psi, the expansion tank is either waterlogged or failed. Turn the boiler off again until you can get that fixed.

    In the meantime, if the pressure relief valve wasn't opening at 30 psi, replace it. It's a critical safety device, and the boiler must not be used until it is known to be working properly.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • lrodptl
    lrodptl Member Posts: 10
    Noticed that with boiler off and water drained,pressure gage drops to just below 20 PSI. Changed reducing valve and gage still reads 20 when cold and 35 when hot. Gage looks like a pain in the **** to change.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,132
    Besides the above advice, I always put my own gauge on the boiler drain (or any drain) to confirm pressure.
    If you drained the boiler, pressure should read 0.
    Follow @Jamie Hall's advice and/or please get a professional out there to help you.
  • lrodptl
    lrodptl Member Posts: 10
    The implication is that the gage reads 20 PSI high and that's why the PRV does not open.
    JUGHNE Member Posts: 10,568
    Have you opened your pressure relief valve several times to test and flush it?