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Thread: Banging heater pipes

  1. #1

    Default Banging heater pipes

    I have this banging in my pipes when the heat goes on. I know it is air in the pipes but do not know how to bleed them! Can you advise?
    Thank you, Dixie

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default banging

    How do you know it is air in the system? Air in a system usually prevents banging, not cause it.

  3. #3
    In the Trades Bob NH's Avatar
    Join Date
    Oct 2005
    New Hampshire


    Two possibilities come to mind.

    Pipes going through wood joists will make noise when they expand and the friction releases. This is usually occurs in the initial stages of circulation.

    I had a problem with my hot water boiler that was making a pulsating hammering. It was caused by steam bubbles in the boiler when it was firing. A steam bubble is created when there is a hot spot in the boiler that exceeds the boiling point temperature for the pressure in the boiler. When that bubble is created and collapses, it makes a hammering noise. It occurs only when the boiler is running. The sound is transmitted through the circulation system.

    If it occurs only when the circulator is running, then it is probably cavitation at the circulator pump inlet.

    You can verify that one or the other of these is the problem by looking at the pressure gauge on the boiler when it is happening. You will see the needle pulsating. You may also see the temperature gauge above 210 F.

    The problem was eliminated by the following changes, all of which contributed a little to the solution.
    1. Increased the pressure just a bit, well within the "green" range on the pressure gauge.
    2. Decreased the maximum temperature setting on the Aqustat.
    3. Changed the firing nozzle from 1.0 Gallon per hour to 0.85 gallon per hour.

    The problem has not recurred since the changes.


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