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Pressure building up

Hi to all. My friend has a oil fired hydronic boiler that is building up pressure to a point where the pressure relief valve opens.He has changed everything from pressure reducing valve to burner control.He has even turned water supply feed off, just to see if valve was feeding, and still the pressure rises. His boiler is oversized, but has worked for years that way without a problem.I even told him to reduce boiler's temperature and still, the pressure rises.Everything is in working order and I'm stumped with this one. Can any of you help with this one?


  • Brad White_203
    Brad White_203 Member Posts: 506
    Oh, sure, Fred....It is always, \"I have this friend...\"

    It is OK, you are amongst friends, tell us the real story....


    I have to ask if there is an old tankless immersion domestic HW heating coil or other source of CW into the boiler. A pinhole leak can do that over time, quite easily.

    The valve you shut off was just the boiler fill line I presume. Check for a second valve. Even if abandoned, sometimes even that valve leaks by. It is best to remove it or at least totally disconnect it. If you "de-pipe" the immersion heater and you get water coming out of it, I suspect you have found your leak. Cap those suckers or better yet remove it when next season comes around.

    If the expansion tank were water-logged, the pressure would rise exponentially as it heats up and the relief valve would go splooey all over your Timberlands.

    My $0.02

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