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Pressure rising to 60psi

I had to replace a leaking expansion tank last week on a radiant heating system. I installed a new one with a 20psi charge and charged the system to 20psi. The water-feed valve was then shut off.

A few days later, I saw the pressure gauge reading of 60psi. Puzzled, I drained around 2+ quarts of water and the pressure went back down to 20psi.

Today, the pressure was high again, so I drained some more. The water temp varies from 100* to 140*.

This all seems wrong. What is happening here?


Steve Garson

Boston, MA
Steve from Newton, MA


  • Jean-David BeyerJean-David Beyer Posts: 2,652Member
    What is happening here?

    Indirect domestic hot water heat exchanger leaking domestic pressure into boiler circuit?
  • Steve WhitbeckSteve Whitbeck Posts: 669Member
    20 PSI

    If this is a standard 30 PSI max pressure boiler the tank should have a precharge of 12 PSI.

    And the most important question is WHY didn't your relief valve trip. If is has a 30 set point it should have tripped. Replace it NOW.

    As far as the pressure gain IF you don't have an indirect domestic water heater ( hole in coil is pushing water into the boiler system ) Then the pressure reducing valve is bad and the shut off valve is letting water leak into the boiler. replace both.
  • unclejohnunclejohn Posts: 1,456Member
    You may

    Simply have a faulty pressure gauge. Relief was not opening? Was the old tank a extrol tank or the old style. And as in previous post why the 20psi charge? Did you connect the new tank in the same location as the old?
  • heatpro02920heatpro02920 Posts: 991Member
    What kind of system?

    radiant with a cast iron oil fired boiler with a tankless water heater for dhw? Gas with an indirect, oil with an indirect, a high pressure tankless with a plate exchanger, ect??? need more info, like was mentioned a boiler with a psi reducing valve and a extrol 30 expansion tank shouldn't be anywhere near 60 with out water pouring from teh pressure relief valve...
  • Steve Garson_2Steve Garson_2 Posts: 634Member
    More info

    The "boiler" is a Bradford-White Combicore water heater.  The expansion tank was and Extrol tank that leaked and replaced with a new one with a 20psi charge. The feed water valve has been shut off, so the additional pressure must be coming from a leak in the coil, with city water coming in gradually, to the tune of 5psi a day recently.

    I need to replace this with something that will last more than five years.  My steam boilers heats a 10,000BTU heat loss hot water loop,  The Combicore heats a 15,000BTU heat loss radiant heated room.  The Combicore has 65,000BTU input. So I will need a boiler to output the combined 25,000 BTU for heating, as well a 45-gallon indirect hot-water tank.

    Any boiler recommendations?  The BTU requirements are so low that I don't think a condensing boiler would ever be cost effective, since I will not be in this house longer than five to ten years, at most.

    Steve from Newton, MA
This discussion has been closed.


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