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Boiler knocks when it starts

bwoodard28
bwoodard28 Member Posts: 7
Hey all - my boiler just started doing this today.

It'll start up, knock around for about 30 seconds, shut off, wait about a minute, boot back up, and repeat the process.  

Here's a video of it happening: https://photos.app.goo.gl/Unr3cDwSTcVWSHw89

Any help is greatly appreciated!

Comments

  • kcopp
    kcopp Member Posts: 4,095
    That is a Laars design boiler. It has a copper heat exchanger across the top. You are not getting flow through the boiler. That sound is steam flashing inside the boiler because it is heating up so fast. More than likely the circulator has failed... I would not use the boiler until this is fixed.
  • JUGHNE
    JUGHNE Member Posts: 10,332
    Agree with kcopp, however how does the steam hammer cause the flame to almost roll out?

    The louder "knocks" coincide with the flame jumping.

    How much pressure is in the boiler when cold?
  • mattmia2
    mattmia2 Member Posts: 7,217
    Dont those burners have an inner structure that sometimes disintegrates?
  • bwoodard28
    bwoodard28 Member Posts: 7
    kcopp said:
    That is a Laars design boiler. It has a copper heat exchanger across the top. You are not getting flow through the boiler. That sound is steam flashing inside the boiler because it is heating up so fast. More than likely the circulator has failed... I would not use the boiler until this is fixed.
    That's what I was afraid of. I've got it shut off for now. Thanks for the insight. 
  • bwoodard28
    bwoodard28 Member Posts: 7
    JUGHNE said:
    Agree with kcopp, however how does the steam hammer cause the flame to almost roll out? The louder "knocks" coincide with the flame jumping. How much pressure is in the boiler when cold?
    5 PSI when it's cold. It's been that way for awhile. 
  • JUGHNE
    JUGHNE Member Posts: 10,332
    Raise the pressure to 12-15 PSI...cold.

    See if the pressure holds there for about 1/2 hour....with no water on the floor.

    You might then, cautiously, try another firing, with your hand on the power switch.

    I have learned it is best to stand off to the side doing some trial run like this.
  • bwoodard28
    bwoodard28 Member Posts: 7
    Update: Replaced the circulator and it works like a champ now. Thanks for all the help!

    PSI still reads at 5. Starting to think I have a bad gauge. 
  • GGross
    GGross Member Posts: 412
    @bwoodard28

    If we attempt to connect the dots, a dead circulator, and a gauge reading low pressure. It sounds like perhaps you had a leak which would lower the pressure and add air, which could potentially have caused the pump to run dry causing premature failure. I would double check the pressure with a new gauge and make sure it is filled correctly to avoid repeating the same failure.
    bwoodard28