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Over pressure valve dripping.....( replaced )

jconlinjr Member Posts: 8
I have been chasing this problem for over a year, I have replaced the back flow preventer, inlet pressure valve, expansion tank and over pressure valve. So when the boiler starts running the pressure slowly rises as the temp rises. In about 15 minutes I am at 30 psi and the pressure slowly rises then the valve starts to leak water into the bucket on the floor. I know it's not a big deal but it just annoys me that it is leaking.
I just checked the pressure in the expansion tank and it is at 15 psi. It's and amtrol ex-15. Do I need a bigger expansion tank? Do I need more pressure in the tank? I did lower the upper temp on the aquastat to 170 but that did not seem to help. I understand when water gets hot the pressure rises.

Any Ideas?


  • Jamie Hall
    Jamie Hall Member Posts: 19,131
    There really are only three possibilities, assuming the pressure doesn't rise slowly when the boiler is off (which would be the feed valve): first, the expansion tank is failed or waterlogged -- but it's only a year old, so that shouldn't be the case (worth checking). Two, the expansion tank is valved off from the rest of the system (it's happened to all of us). Three, the expansion tank is just plain too small. Go to https://www.amtrol.com/resources-rewards/selection-tools/ to check the size.

    Oh -- and plan to replace the pressure relief valve. Once they've operated a few times, they'll always be suspect -- and they're cheap.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • jconlinjr
    jconlinjr Member Posts: 8
    I have no idea how many BTU's the boiler is. It was here when I moved in. I think your right the expansion tank is too small. It has a EX15 and I think I need and EX30.
  • jconlinjr
    jconlinjr Member Posts: 8
    Oh BTW I changed the PRV yesterday....
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 3,318
    edited December 2019
    One more possibility IF your oil boiler also heats your water. Is the domestic water pressure passing through the heat exchanger coil? Disregard this if you don’t hear your water with the same boiler

    Regarding the BTU. If you know the firing rate gallon per hour or nozzle size we can help you with the BTU.
    Edward Young
    Retired HVAC Contractor from So. Jersey.
    Services first oil burner at age 16
    P/T trainer for EH-CC.org
  • It can be very frustrating chasing down high pressure problems. Everything gets changed and it's still happening. In your case, yes, the x-tank may be too small for your system.

    Another thing that might be causing this problem is how the expansion tank is connected to the system piping. There could be a clog in the piping preventing the system from "seeing" the x-tank. Perhaps a galvanized nipple that is solid with debris or even a microbubble air separator clogged where the x-tank is connected to it. Spirotherm air separators seem to be prone to this.
    Often wrong, never in doubt.
  • jconlinjr
    jconlinjr Member Posts: 8
    I removed the domestic water system 3 years ago, so the boiler is only used for heating the home. I had a leak and replaced all the pipes connecting the house water supply to the boiler and the pipes connecting the expansion tank, all new.
  • jconlinjr
    jconlinjr Member Posts: 8

  • jconlinjr
    jconlinjr Member Posts: 8

  • jconlinjr
    jconlinjr Member Posts: 8
    So I checked on the amtrol web site and used there calculator for tank size and for the smallest boiler of 50,000btu they recommend an EX30 tank, I would guess that this boiler is 75,000 and that too would be and EX30 tank. I had a service guy in 2015 in and he changed the tank and put in a EX15. The reason he was here was water coming out of the OPV, and changed the tank and the valve and left. Never solved the problem. I called him and told him that. He was like oh well.... So for the last 4 years I have lived with this problem.
    JUGHNE Member Posts: 9,819
    The EX30 might be longer and not fit where the 15 is.
    You can gain room by shortening the nipple above the tee that has the gauge.
    Even better is to put the gauge tee between the water fill valve and the air separator. Then maybe add an isolation valve for the tank. You could then remove and check pressure without draining much of the system.
    The charge is checked before the tank is ever installed.
    Best way, no guessing then.
  • Looks like a lot of rust on the nipple end of the x-tank. Only an observation.

    Change the x-tank to the larger size since it's pretty easy to do. While you're at it, stick a pencil up the that 1/2" black tee and see if there's any debris in the air eliminator.

    What kind of heating system do you have? Radiators? Radiant?
    Often wrong, never in doubt.
  • jconlinjr
    jconlinjr Member Posts: 8
  • The x-tank is in a perfect place to pick up any debris that flows through the system. It's a drip leg.
    Often wrong, never in doubt.
  • hot_rod
    hot_rod Member Posts: 16,517
    Or add a second #15 tank. Pipe them to the side, not directly below the purger if is clogged with crud
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • If your system was a gravity conversion, it will indeed need a larger x-tank because of the large pipes and the increased water capacity.
    Often wrong, never in doubt.