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Loud bang as pipe cools

brogama Member Posts: 12
Recently noticed that with my baseboard heat system that after the boiler shuts off and maybe 30-40minutes later there is one loud bang of a pipe. Confusing because it seems to be when the system is cooling.  And, I haven’t been able to cycle the noise on and off. I believe the pump is still circulating at this time.  Any ideas of where to start?


  • Jamie Hall
    Jamie Hall Member Posts: 16,068
    Most likely an expansion noise -- and yes, expansion works both ways (expanding when getting warm, getting shorter when cooling of). Question is, what's hanging up and where? They can be difficult to track down -- but look for anywhere the pipes are touching or hard up against something.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ethicalpaul
    ethicalpaul Member Posts: 3,043
    I have one of these right now. In my case I'm quite sure it's due to high tension in the vertical direction between a radiator and the main. Look for places where there is tension between different parts of your main or your main and baseboards. Just like Jamie said, it can be hard to find.

    I think mine got introduced when I attempted to put a correct pitch on my main--one of my radiators does not have a proper swing joint on it and the radiator is basically holding up part of the main now. To be addressed when I get a minute haha
    1 pipe Peerless 63-03L in Cedar Grove, NJ, coal > oil > NG
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