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banging hot water boiler

I have a 175,000 BTU Weil Mclain boiler, hot water heat. The boiler started to bang when it got up to temperature. I replaced the 1/8" air vent at the top of the boiler with a 3/4" Junior Spirovent. The banging quieted down a little but it still is banging. Any suggestions?


  • DZoro
    DZoro Member Posts: 1,048
    Pic of the system would help. What is the boiler pressure? What type of expansion tank? A couple questions but some pics will tell us much more.
  • kcopp
    kcopp Member Posts: 4,432
    Whats the temperature?
  • SuperTech
    SuperTech Member Posts: 2,159
    What temperature is the aquastat high limit set to? What temperature is the boiler gauge showing when the burner shuts off? What about the boiler water pressure? What is it when the boiler is cold? (If it's cold start) what is the pressure when the burner shuts off on high limit?
    Do you have more than one zone? If so, are they controlled by zone valves or multiple circulators?
    Pictures of the boiler and piping would really be helpful in assisting you.
  • clammy
    clammy Member Posts: 3,111
    Do you know if this boiler has been taking on make up water ? I would suggest testing your boiler water for total devolved solids or tds . If your reading are high you may have lime and calcium and or scale build up on the walls of your boiler which will cause the boiler to percolate and bang . There are chemicals which in some cases will quite it down and in worse cases the boiler will have to be de scaled using a chemical and then flushed out . You should make sure you do not have any small leaks which would in turn add more fresh water . If you have any leaks repair also test your portable water for it tds level if hi add a demineralizer filter to it feed line for your boiler . Testing fill water on both steam and hot water boiler is something not many do until there is issues better to do before when the system is being installed it prevents issues in the future being de scaling or de liming a boiler and filling w quality low tds water and adding a hydronic inhibitor should be a standard as it is in most of Europe . As time goes on we can all except to see poor water quality and higher tds reading and of course hi chorine levels and what ever else the water companies add as treatment . Peace and good luck clammy
    R.A. Calmbacher L.L.C. HVAC
    NJ Master HVAC Lic.
    Mahwah, NJ
    Specializing in steam and hydronic heating
  • Big Ed_4
    Big Ed_4 Member Posts: 2,785
    Sounds like its breaking into steam ... Check the aquastat
    I have enough experience to know , that I dont know it all