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Boiler noisey only when heating water?

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Hello all,
I am not very experienced with heating systems and i am having a problem i can not figure out. I have a natural gas boiler that heats my house and my domestic hot water. There is 3 zones; "Main level" "Basement" "Hot water". All zones come from the same place and are pumped by the same circulating pump. However, whenever i use hot water and my tank calls for heat, after awhile (5-15min) my system just starts banging like crazy. Kind of sounds like it is coming from the expansion tank but it is hard to tell for sure. It does not do it when the other two heating zones call for heat, only when heating hot water. The way i understand it was put together, the hot water heater is just another loop so i dont understand why it is only doing it when heating the water. Any ideas?

Comments

  • kcopp
    kcopp Member Posts: 4,448
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    What do you have a for a boiler?
    If it a Modulating gas boiler the boiler typically will ramp up to full fire to make hot water.
    When space heating is on that heats the water up to match the water temperature needed based on an outdoor reset curve.... So unless its super cold out the boiler may not need to go into full/ high fire.
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
    edited February 2020
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    There should be a high limit aquastat on the domestic hot water heating circuit. It may be set too high and allow boiling to occur.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • HunterHaav
    HunterHaav Member Posts: 2
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    > @Jamie Hall said:
    > There should be a high limit aquastat on the domestic hot water heating circuit. It may be set too high and allow boiling to occur.

    The stat is set to 120°F, that's pretty standard right?
  • JUGHNE
    JUGHNE Member Posts: 11,102
    edited February 2020
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    The 120 is what the boiler will heat the indirect tank up to for your DHW use........but the boiler may supply 180 thru the tank coil to do so.

    There would be a control on the boiler to lower that 180 down,
    but if the water flow thru the boiler is too slow for 180, then boiling water could happen.

    Pictures of the boiler, piping and water tank would be good.