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Boiler -foghorn sound at start up

kdean2001 Member Posts: 1
edited February 2022 in Radiant Heating
I have been researching this foghorn sound my boiler makes when the system calls for heat. It sounds like it’s coming from the vent outside.  I have read it’s as easy as drilling a hole in some location.  I say some location because I’m not at all familiar with boilers.  A tech told me it was a 1200 dollar part.  That is a very big difference.  Is there anyone familiar with this sound?  Thanks


  • neilc
    neilc Member Posts: 2,708
    post a general distant picture of the boiler, with the circulator(s), and zone valves,
    someone will see something
    known to beat dead horses
  • GroundUp
    GroundUp Member Posts: 1,924
    A model # of the boiler would be handy also
  • Mark @ Radiant Works Inc
    I have someone put a combustion analyzer on it. Sounds like your air fuel mixture is off
  • Ironman
    Ironman Member Posts: 7,377
    If it’s a mod/con boiler, it has a negative pressure gas valve and burner. The use of CSST gas tubing can cause the fog horning.

    Sometimes, adjusting the fuel mixture to the richest spec in the manufacturer’s I/O manual will alleviate it, but a knowledgeable tech with a combustion analyzer will be needed. If that  doesn’t correct it, the CSST would have to be replaced with a larger size or with hard pipe.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.