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relief valve

jpatch Member Posts: 1
during winter, each time the furnace fires, upon reaching setting temp and hot water is ready for circulation, the relief valve releases some hot water onto basement floor. what is happening. is the valve shot ? Or is the temp setting on boiler off...


  • Intplm.
    Intplm. Member Posts: 1,443
    Please offer more info as to the type of relief valve. A picture up close maybe, and a pic or two showing what it is installed on.
  • Jamie Hall
    Jamie Hall Member Posts: 21,117
    Neither one. But the expansion tank is. It may not actually be shot -- it may have just lost its air charge. Either way, it's not doing its job. Depending on how its piped and valved, it may or may not be simple to check: the procedure is to reduce the water pressure in the tank to zero, and check the air pressure in the tank (there is a Scharder valve on the end opposite the inlet to do that) -- the air pressure should be the same as the system static pressure. The joker is reducing the water pressure to zero... some systems are piped so that the tank can be valved off the system and disconnected or drained. If so, it's not hard. If not, you have to drain the system... and then refill and purge it. Which is a bore.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnNY
    JohnNY Member Posts: 3,152
    My money's on you needing a new expansion tank.
    Contact John "JohnNY" Cataneo, NYC Master Plumber, Lic 1784
    Plumbing in NYC or in NJ.
    Take his class.
    Intplm.Zmandelta T
    HVACNUT Member Posts: 5,034
    edited May 2019
    Or if the expansion tank is a big barrel looking thing in the ceiling joists above the boiler, it might need to be drained.
    A pro should look over the whole system to make sure its safe.