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Jjacobs Member Posts: 1
relief valve blowing off.not consistently but daily and quite a bit of water.new relief valve.aquastat set low 160 high 180 diff 15.circ pumps correct flow and working as should.reducing valve and relief valve and expension tank on supply line.cold supply turned off. Please help.thank you


  • Have you checked the pressure of your expansion tank (x-tank)? It should equal the normal fill pressure of your system.

    To check the pressure of your x-tank, it should be at zero PSI from your system. You either have to drain your piping or, if you're lucky and have a valve between your x-tank and your piping, turn the valve off, take the pressure down to zero and check the pressure of the x-tank at the Schrader valve.

    It could also be that your x-tank is too small.
    Often wrong, never in doubt.
  • mikeg2015
    mikeg2015 Member Posts: 1,187
    What pressure is it normally at? What is the max pressure. Turn it to 190F and see what the pressure is.

    Do you have a domestic water heater on it? Any chance the coil is leaking?

    Most likely expansion tank is bad. But after it blows off once it shouldn’t trip again and again If fill valve is closed.
    HVACNUT Member Posts: 4,594
    Does the boiler have a tankless coil or indirect water heater?
    Could be a pin hole leak pushing street pressure into the heating system water.
    See if you can isolate any domestic water from entering the system and see if the pressure holds steady. Maybe overnight and check the pressure in the morning.