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Choosing correct pressure relief valve

HenryL Member Posts: 1
My system has a 30 psi pressure relief valve that will always leak.  I changed this valve multiple times thinking it's faulty directly from manufacturer.  I set the cold water pressure at 14 psi, I set the expansion tank(new) at 15 psi.  My boiler plate states 50 psi as the Maximum Water Pressure.  Can I change to a 50 psi pressure relief valve?  The only reason I installed 30 psi valve is because it was the one installed when I bought the house.  It was leaking from the top, and pressure relief onto the floor when I turn on the heater in the beginning of the season.


  • Jamie Hall
    Jamie Hall Member Posts: 23,445
    You're looking at the symptom, not the cause. A hot water system with a cold pressure of 15 psi should not go over about 20 psi when fully hot. That's the job of the expansion tank. It's not doing its job.

    The 30 psi relief valve is the correct valve for the application -- but as I say, your problem isn't the valve.

    Did you set the tank pressure when it was disconnected from the system? And then connect it? And what does the pressure on the Schrader valve read now? Are you sure that any valves between the expansion tank and the system are open? I know it's obvious -- but we all overlook things now and then.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    JUGHNE Member Posts: 11,077
    How tall is the building?
    Are the radiators and piping huge, your tank may not be large enough.
  • pecmsg
    pecmsg Member Posts: 4,893
    What does the pressure gauge read?
  • neilc
    neilc Member Posts: 2,708
    does this weepy boiler also heat your domestic hot water?
    known to beat dead horses
    EBEBRATT-Ed Member Posts: 15,629

    Expansion tank, leaky water feeder and leaking tankless or indirect coil are the first 3 things to check.

    I would not put a relief valve rated more than 30 psi on it
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,109
    If the boiler rating plate reads maximum working pressure 50 PSI then you can use a 45 or 50 PSI rated relief valve. Most boiler are rated for max working pressure 30 PSI and therefore most plumbers carry 30 PSI relief valves on the truck. As long as you don't have a 5 story house and the cold static pressure is 12 PSI, the 30 PSI relief valve should be no problem. So do what @Jamie Hall suggested. Check for the cause of the boiler pressure rise.

    Sometimes a more powerful circulator is installed on the return pipe of the boiler. When the pump comes on the boiler pressure may spike and cause a little squirt at the Pressure Relief Valve until the initial startup shock to the system is equalized and things run smoothly. Every startup will have that squirt so you may need to see if your pump is oversized. If it is the correct pump and the correct size expansion tank, and the pump is places in the correct location in the system, and you still have the problem, then you may need a 45 PSI valve. It all depends on how the system was designed. If someone paid extra to get a boiler rated at 50 PSI working pressure, there must be a reason.

    You need someone who understands your system and how Static pressure and Head pressure work in a system. This may not be a simple job for a rookie plumber. You may need to call out the cavalry on this one.

    Mr Ed

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?