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Banging from primary pump

3zht
3zht Member Posts: 18
Hello all,
My Lochinvar Knight boiler had been working great but lately it keeps making the pipes bang which can be heard upstairs. I went into the basement and filmed it to give you folks a better idea of what's happening.

It seems like the primary pump keeps turning on/off on it's own even when the Tstats aren't calling for heat. The primary pump starts up and then shuts off immediately and it repeats for several minutes. The pump also gets super hot to touch as well. The only way I can get it to stop is to kill the power to the pump and boiler with the emergency switch. Any ideas?

EDIT: this site won't allow me to upload the video

TIA

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 8,857
    Don't know if the pump motor has an internal overload in it that could be shutting the pump off. How hot is the motor can you hold your hand on it?
  • hot_rod
    hot_rod Member Posts: 14,755
    If the burner is firing, the pump needs to be circulation. The banging could be the water boiling inside. The pump is water lubricated, it should run a bit warmer than the fluid circulating. Is the pump powered from the boiler board or another relay box. Check voltage at the pump when it starts banging. It sounds like something is causing you to lose flow. Is it purged well, and air pocket will also cause flow to stop and an over-heat condition.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    HomerJSmith
  • 3zht
    3zht Member Posts: 18
     The pump motor gets too hot to touch as some points. Other days of the day when it’s working properly it’s warm but I can rest my hand on it. 


  • 3zht
    3zht Member Posts: 18
    @hot_rod the burner isn’t firing that’s the odd part. The boiler isn’t even running and the pump is going on/off. 
  • HomerJSmith
    HomerJSmith Member Posts: 1,286
    edited March 17
    Is the pump an ECM pump? What is the pump model #? The primary pump is on the primary circuit going to the heat emitters, the secondary boiler pump is on the secondary circuit. Take a photo of your sys.
  • Erin Holohan Haskell
    Erin Holohan Haskell Member, Moderator, Administrator Posts: 1,590
    3zht said:


    EDIT: this site won't allow me to upload the video

    @3zht, please upload your video to YouTube and share the link here. Thanks.
    President
    HeatingHelp.com
    ethicalpaul
  • hot_rod
    hot_rod Member Posts: 14,755
    3zht said:

    @hot_rod the burner isn’t firing that’s the odd part. The boiler isn’t even running and the pump is going on/off. 

    Some of the small mod cons can be tricky to purge all the air out, I'd guess the pump gets air locked occasionally. It should never get smoking hot, just a bit warmer than the fluid it is flowing. They will seize up if they get hot, boil the water out of the rotor can, and run the bearing dry.

    Some circs have a screw in the motor to burp air out, try that when it is hot. Sometimes the screw is hidden under the manufacturers label (Grundfos) , if you snap it off.
    I've also burped them by loosening the flange bolts or the allen bolts holding the motor into the volute.

    The hot pump, banging, stopping of circulation together tend to make me think an air problem. It is an easy test and fix, if so.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
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