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pressure relief valve problems!

mark_103 Member Posts: 7
I have a large home in the northeastern part of the country and I have three seperate natural gas boilers all piped in tandem that opreate the heating system and domestic hot water system. Last year I had a problem with 2 relief valves dripping water. Plumber came and found expasion tank waterlogged and replaced it and installed two new 30# relief valves on boiler # 1 and # # 3. Everything was ok. A few days ago, boiler #2 started leaking water out of relief valve and plumber came to install new valve. New valve was installed and after a few days, started leaking again. Pressure on boiler #2 reads 16lb. Why is new relief valve sitll leaking? Can it be deffective? Note the boiler that is leaking runs my domestic hot water and a small zone. Can you help.


  • RobbieDo
    RobbieDo Member Posts: 131
    Expansion tank

    How is the expansion tank on the one that's leaking? What is the pressure in the tank, is there water in it?
  • mark_103
    mark_103 Member Posts: 7

    hey Rob. There is only one large expansion tank controling all three boilers. # 1 is not leaking and # 3 is not leaking. Why is # 2 leaking? Go Figure?
  • Jamie Hall
    Jamie Hall Member Posts: 21,117

    pressure relief valves are also temperature relief valves -- could that be?  And could that one boiler be overheating?

    Are there any check valves on the system between the boilers and the combined header (and pressure tank)?  Or other valves?

    Of course, there is always the possibility that the new valve is not working right, too...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • mark_103
    mark_103 Member Posts: 7
    check valves

    On boiler #1 #2 #3 there are b+g flow controls on each feed. Boiler # 2 [ the problem child ] Temp is set at 180. no check valves on return on all 3 boilers. How can this boiler be running at 16 Lbs. and leaking water at releif valve when other boilers are running at same pressure and same temp are not leaking? dont want to go and install another 30 # valve on boiler #2 and have It leak again.
  • Gordy
    Gordy Member Posts: 9,537
    Have you tried

     To burp the valve to see if it will seat. May be some dirt got in it when it was installed, or if he tested it after installation, and some sediment got on the seat.

     If the boiler is reading 16psi that rules out a leak on the domestic side HX.

     Could ba a bad valve never say never these days.
  • mark_103
    mark_103 Member Posts: 7
    valve problem!

    I guess Its worth a try, But can you se me missing anything else other than a bad valve? Cant figure it out but will try.
  • Eric_32
    Eric_32 Member Posts: 267
    I would confirm the pressure...

    With a pressure gauge that will screw on a hose bib for that boiler and confirm the pressure in that boiler. Look for a gauge that has 2-hands. One records pressure, the other is a            re-settable maximum pressure hand stays at the water system’s highest pressure point during the test period.

    You can leave it on and it will record the highest pressure it got to incase the problem happens when you are not there. If the pressure is less than the rating of the relief valve it should not be leaking.

    Something like the Watts 276H300 below except the 300psi scale on the gauge isn't the best for testing boiler pressure. Lower scale would be better.

    Water Pressure Gauge w/ Hose Connection 0-300 PSI with red max indicator Series 276H300
  • Brad White
    Brad White Member Posts: 2,393
    I usually stand back

    and look at it from the original intent of design.

    When relief valves weep or discharge, especially multiples, I tend to think that is too much of a coincidence. They may just be doing their jobs!

    Rather, I would make an estimate of system volume and see if the expansion tanks are selected appropriately in the first place. It is not uncommon to see original gravity HW systems made into closed systems and with new expansion tanks at lower elevations.

    There is a lot of water in those systems, sometimes hundreds of gallons. Think of it from scratch and see how big your tanks really need to be.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
  • icesailor
    icesailor Member Posts: 7,265
    Leaking PRV's

    Brad made my point.

    Just because they are supposed to relieve at 30# doesn't mean that they all will at the same time and pressure. The older valves may have inherently opened at a slightly higher pressure. The ones opened at a lower pressures are the ones that had seat failure and were replaced. The new ones opened at the same pressures.

    I have an account that is a commercial building with 3 W-M WGO-7's. It is P/S and has a properly sized expansion tank on the ceiling. It has a gauge glass on the end of the tank. You can visually check the water level in the tank. When it is getting waterlogged, there is always one PRV that starts the first leaking when the system rises in temperature. It has been doing it for the last 22 years that I have been working there.

    If you want to prove or disprove the theory of too small expansion, turn on all the heat loads on all the boilers and get the system as hot as it will get. High limit is best. You must do this after you replace the leaking PRV. Watch the pressure gauges. If the pressure in the system starts climbing, and gets over 25# and heads to 30# and the system isn't up to high limit, wait until a PRV valve starts to drip. If it went to 30#, it shouldn't have. Take the load off the system. Shut off the fill valve. Let the system temperature drop to as low as it would get when cold or normal. If the temperature drops to below the PRV/Fill Valve, and the system pressure goes below the PRV setting (usually 12# but may have been set higher), the expansion system is too small. It is adding water when it is cold and getting rid of it when hot. I've often added a #60 Extrol to the system and it solves the problem.

    If you figure out how many gallons of water are in your system, Amtrol has calculators that tell you what size pressure/expansion device to use.
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