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boiler pressure drops to zero with little water loss

sunlight33 Member Posts: 330
edited May 30 in THE MAIN WALL
Today I went home and saw the boiler pressure gauge at 0, so I turned the water feed valve on (normally I leave it off) and the pressure quickly went back to 12 psi but with hardly any water added. I checked for leaks but didn't find any. Then I flipped the PRV on the boiler, the pressure went from 12 to 0 in an instant with only a small amount of water discharged. What does this mean?

Update: I reduced the pressure in the expansion tank from 16 psi to 12 psi, now it seems to be normal.


  • mattmia2
    mattmia2 Member Posts: 3,168
    It would have worked fine that way, it just would have gone up to 16 psig quickly then risen more slowly as it continued to heat. The auto water feed is shut off or not working if it didn't stay at whatever the prv is set for and either there is a small leak or some air got vented through an auto vent.
  • gennady
    gennady Member Posts: 822
    edited June 2
    The expansion tank pressure should be equal to system static pressure plus at least 5 psi. Charge tank when water is fully drained from the water side of the expansion tank and open to the atmosphere.
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