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Pressure Relief Valve Opens

On Friday and again this morning, my Weil Mclain (Model SGO-Series 2) steam boiler's pressure relief valve went off. When it happened on Friday, I replaced it and it was OK over the weekend, but it went off again this morning. The relief valve is specified at 15 lbs, but the pressure gauge on the boiler only showed four pounds of pressure, which is typical for this unit. It's working again at the moment, but something is up with it! Anyone have any suggestions as to what the problem might be?? Thank yo.


  • pecmsg
    pecmsg Member Posts: 4,193
    Clean the pig tail under the pressure gauge / pressure control
  • Jamie Hall
    Jamie Hall Member Posts: 21,541
    Four pounds of pressure shouldn't be enough to open the pressure relief valve. On the other hand, it's way too much for a residential steam boiler.

    So... check the settings on the pressuretrol. It should cut out at 1.7 psi and back in at 0.7. Remove and clean out the pigtail for the pressuretrol to the boiler. It may be clogged. Check that the pressure gauge returns to zero when the boiler is cool (it would be good to add a 0 to 3 psi gauge on the pigtail for the pressuretrol, but not absolutely necessary).

    And I would replace the pressure relief valve. Once they have operated, while they are supposed to be able to function properly again, that is your last line of defence against catastrophe, and they aren't expensive...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • pecmsg
    pecmsg Member Posts: 4,193
    pecmsg said:

    Clean the pig tail under the pressure gauge / pressure control

    I'd believe the safety before the gauge!
    ethicalpauldelta TSuperTech
  • ethicalpaul
    ethicalpaul Member Posts: 4,821
    Especially two of them! This is not good!
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
    delta TSuperTech
  • Intplm.
    Intplm. Member Posts: 1,470
    Debris in the boiler water might be getting between the seat and the washer on the relief valve.
    When you change it again. And you should, just to be safe.
    When the old one is removed run a good amount of water through the port that the relief valve is threaded on to clearing any potential debris. Then put the new one on.


    Run a lot of water from the one installed now, and then replace it with a new one. Try to get the water to run as clean/clear as possible.
    JUGHNE Member Posts: 10,792
    Intplm, this is a steam boiler. Water should not reach the pop off valve.
    He truly has a high pressure control problem.

    Clean pigtail...check control operation and get a new 0-3 PSI gauge.
  • Intplm.
    Intplm. Member Posts: 1,470
    @JUGHNE Good catch. thanks.