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presure valve leaking, dripping

dbwdbw Posts: 3Member
Your writing is delightful! I have a baseboard hot water system that constantly leaks out of the pressure relief valve. I have replaced the valve two or three times without much effect. Some times if I add air to the expansion tank (it is small, maybe 2 or 3 gallons ) the valve will stop dripping. is it my expansion tank that is contributing to this problem, or something else?

Comments

  • STEAM DOCTORSTEAM DOCTOR Posts: 924Member
    Probably need new expansion tank. Have you checked the pressure gauge while boiler was running?
  • HomerJSmithHomerJSmith Posts: 591Member
    edited May 19
    Shake the X tank if it feels sluggish it is probably water logged. You can also remove the plastic cover on the Schrader valve (tire valve) on the bottom of the tank and depress the stem quickly and if water comes out it needs replacing. If it is more than 10 yrs old, it probably need replacing.

    If your system has an Amtrol tank #110 fil-trol, the system pressure is set by the air pressure on the air side of the tank, if not, it has a separate fill valve on the cold water input to the boiler which sets the system water pressure. Look at the pressure gauge on the boiler and see what it reads. If it is close to 30psi when the boiler is cold, when the boiler heats up it may push water out of the PRV and overload the air charge in the X tank. That means a faulty fill valve, especially if there is no adjustment because of failure of the valve.

    If the boiler cold pressure is between 12 to 19 psi and you lose water from a cold boiler that means that the PRV could be faulty.

    IF you replace the X tank, replace the PRV. too. If you need to replace the X tank and you are going to do it yourself check back for advice as it has to be done properly. I'm assuming that your setup was working properly and over time it is not working now.
  • When you check the pressure on your expansion tank, it should be free of system pressure, otherwise you will get a false reading.
    Often wrong, never in doubt.

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  • JUGHNEJUGHNE Posts: 6,026Member
    Perhaps we should clarify some terms.
    IIRC a PRV is a pressure reducing valve....auto water fill device to set pressure at usually 12 PSI.

    A pressure relief valve, some times referred to pop valve or simply relief valve is set to typically 30 PSI for hot water boilers.

    When your relief valve passes water, it is doing its job and not necessarily defective if it reseats when the pressure is lowered to correct levels....it opens to prevent damage to the boiler or quite simply the entire boiler exploding and going literally thru your roof....yes, serious as a heart attack! ….this happens in this country a few times a year.

    Most likely your tank is water logged and needs replaced.
    If your PRV is defective or out of adjustment it can add more city water to the system and increase the pressure to open the pop relief valve.
    Simple fact is that you can not compress water. So when the water temp rises and it expands it's volume, it will compress the air in the tank....if there is any left.
  • HomerJSmithHomerJSmith Posts: 591Member
    edited May 19
    Ya, both a PRV (pressure relief valve) and a PRV (pressure reducing valve) (fill valve) have the same initials. Gad!

    If the pressure relief valve has been popping for a long time and it doesn't have the isolation diaphragm between the seat and spring it could be rusted or fouled. They're cheap, saves problems later.

    Water is compressible, a Black Hole does it quite easily.

  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,035Member
    @dbw

    The question is do you have a diaphragm expansion tank or a plain steel compression tank? Can you post a picture?
  • JUGHNEJUGHNE Posts: 6,026Member
    As the OP stated above this is his 3rd or 4th pressure relief valve, so the last one should be usable if things are corrected.
    As long as it open and reseats when tested "once a year" as recommended.
  • HVACNUTHVACNUT Posts: 2,523Member
    > @HomerJSmith said:
    >
    > Water is compressible, a Black Hole does it quite easily.

    ???
  • JUGHNEJUGHNE Posts: 6,026Member
    edited May 19
    Only on Star Trek. B)
  • Larry WeingartenLarry Weingarten Posts: 1,586Member


    Yours, Larry
  • dbwdbw Posts: 3Member
    Thanks, I will look deeper into this. Depressing the Schrader valve did not result in water coming out, I also did not hear any air coming out.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,035Member
    @dbw ,

    No air and no water means replace the tank. The diaphragm is bad. You could recharge it with air at 12 psi temporally but It will not hold. Since you have to remove the tank to repressurize it you might as well replace it. They are not very expensive
  • @EBEBRATT-Ed "No air and no water means replace the tank. The diaphragm is bad."

    Agreed, replace the tank because it's probably old and it makes sense to install a new one, but don't agree that the tank is bad. It just lost its charge, no?
    Often wrong, never in doubt.

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  • EBEBRATT-EdEBEBRATT-Ed Posts: 6,035Member
    @Alan (California Radiant) Forbes

    Diapharam tanks loose a little air through the bladder every year. So it's possible he could recharge it and make it work at least for now.

    I am just thinking the cost of the tank versus draining and refilling...there is probably no valve to isolate the tank so is it worth all the draining and filling and bleeding to recharge the old tank and then do it again to install a new tank?
  • hot_rodhot_rod Posts: 11,858Member
    You can also rap on the side of a tank with your knuckles to determine if the tank is waterlogged. Any idea how old it is?
    It may be one of the least expensive components to replace, if it is defective, add service valve for the next person that may have to check or replace it..
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • hot_rod said:

    You can also rap on the side of a tank with your knuckles to determine if the tank is waterlogged. Any idea how old it is?
    It may be one of the least expensive components to replace, if it is defective, add service valve for the next person that may have to check or replace it..

    Add a union and a hose bibb as well. The next guy with thank you.
    Often wrong, never in doubt.

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  • dbwdbw Posts: 3Member
    thanks, the system is at least 20 years old. many of the zone valves were replaced since 2002. each of the zones can be turned off at both ends of the run and drained independently. Also the water can be turned off before the pressure regulator for the whole system
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