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Pressure Relief, What Am I Missing?

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Rick @ young supply saginaw
Rick @ young supply saginaw Member Posts: 3
in THE MAIN WALL
The pressure was 15 to 16 all the time I was there. boiler cycles at 170 deg and pressure never was higher than 16

Thanks for your input
Rick

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  • Rick @ young supply saginaw
    Rick @ young supply saginaw Member Posts: 3
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    blow off only when I am not there

    What am I missing? Hot water boiler system with 3 zone valves on the supply side and pump on the return.
    (not pumping away) Supply water is piped to an auto fill valve between the scoop and the exp. tank, both the fill valve and the exp. tank were changed on the first service call along with the pressure relief valve. Boiler is approx. 20 plus year old dunkirk 187,000 input. My contractor treated the boiler system with 8-way boiler treatment. System ran for 2 days then was drained and treatment added again. Relief valve still blowing off.
  • Brad White_9
    Brad White_9 Member Posts: 2,440
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    A few things come to mind

    1. You are not there! Of COURSE it waits... :)

    2. Expansion tank is too small or has ruptured/leaked it's charge. Is this installed in a converted gravity system with large pipes and radiators?

    3. Fill valve not calibrated; may slow but not stop filling until kablooey-time. (Forgive Scientific Jargon). Then it fills again. Slow leak-by is what I am thinking. Try manual isolation and see what happens.

    4. Is there a tankless coil? Might that have a pin-hole leak that also would fill the boiler-side with domestic-side pressure? Again, slow leak.

    What is the initial cold fill? Any idea of system volume relative to the expansion tank?

    All I have for now-

    Brad
  • lchmb
    lchmb Member Posts: 2,997
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    One other thought

    One other thought to be added into the great idea is the aquastat. If it is not sensing properly on a long call the unit could be overheating.
  • [Deleted User]
    [Deleted User] Posts: 0
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    Is there...

    a high pressure drop item in the zones, like say an Amtrol DHW tank?

    If there is, I will speak. If theres not, all I can say is move the pump, leave everything else as is and your problems should go away...

    ME
  • Rick @ young supply saginaw
    Rick @ young supply saginaw Member Posts: 3
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    thanks for your thoughts

    Thank you for your thoughts on this problem job. I made a comment to the contractor about the size of the expasion tank but the answer I got was that size worked for 20 years before I had to change it. The piping change was not an option to move the pump to the supply side because of homeowner not willing to fund a project of that size.
    Thanks again
    Rick
  • Uni R
    Uni R Member Posts: 663
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    Expansion Tank

    Did you ensure that the expansion tank was pre-charged to the proper system pressure?

    It would be nice to know what temperature the boiler is running when the PRV trips. What's the pressure when it is cold and when it is 180* or maximum normal temp?
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