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One loud knack only

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[Deleted User]
[Deleted User] Posts: 0
in THE MAIN WALL
Burnham MPO-IQ 84 oil burner, two HW baseboard Zones and Amtrol 41gal IDW Heater set for priority. The system is piped according to the Burnham Manual. One circulator and two zone valves for heat and one circulator and no zone valve for the DHW. At times, unpredictable, I can hear one loud knack in a baseboard pipe. It starts with the heating circulator running and a zone valve open. At that time the burner has not fired. After this one time loud knack the system runs fine, and no more knack till may be 3 or 4 or ?? heating cycles. Help
Hilmar

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  • BobC
    BobC Member Posts: 5,479
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    Something getting restricted when it's trying to expand? Look around for something that looks like a sausage fit and add some milk jug shims where it seems appropriate.

    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • icesailor
    icesailor Member Posts: 7,265
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    Define the "Knack" (Knock?)

    Does it sound like someone or something beat on a pipe? Or does it sound like something moved inside the house framing when the weather changed?

    It sounds like it is pipe expansion when the system is cold, and has contracted back to its cold condition. When the circulator starts and starts pumping hot water throughout the system, pipes expand. If they aren't supported as they pass through framing members, and they were allowed to rest on the wood rather than cradled in a hanger, they creak across the wood as they expand and make a noise. I never used plastic milk jugs for strips. That would work. I used about every other thing from plastic Mickey Mouse eared hanger clips to copper or lead flashing strips. You have to locate the spot. Often by just looking for places where the pipes are rubbing on the wood.

    For the DIY/HO though, you can take a can of Silicone Spray with the tube, and spray around any pipes that you think are rubbing. Enough so that the liquid gets on to the bottom of the pipe. If it gets better, then its pipe rubbing.

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