pipe knocking

Discussion in 'Plumbing and Central Heating' started by Tomswan, 15 Oct 2021.

  1. Tomswan

    Tomswan

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    I realise there are threads around this, but I haven't found the symptom I have, so maybe someone will be able to point me in the right direction.

    After the central heating has been on for a while a loud rapid fire knocking starts. It stops the instant I turn the tap on (have been turning hot water tap on and don't know if it would also work if I turned cold water tap on).

    I let the tap run for a bit, then turn it off. Sooner or later the loud noise starts again and I have to repeat the process.

    The only way to stop it for good is to turn off the central heating (combi boiler).


    I thought it might be an air lock. I bled all the radiators this morning but no air came out.

    Any suggestions?
     
  2. CBW

    CBW

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    Sounds like a failing float valve in the feed and expansion cistern, unless you have a sealed system/Combi boiler?
     
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  4. Tomswan

    Tomswan

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    It's a combi boiler. I can have the central heating on for
    hours with no noise, but then it will start. I thought it might be heat related. I don't have a thermostat in the house, although the temperature on the boiler is not set very high.
     
  5. CBW

    CBW

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    Does the pressure rise at all, or do you lose pressure frequently? What make/model of boiler?
     
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  7. Tomswan

    Tomswan

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    I haven't been keeping tabs on it. I have just had a look and the pressure is 1.5, dead in the middle of the green.
    It's a Worcester heatslave 2.

    Ive got the hot water on now and there is no noise. I will leave it on to see if a noise starts up without the central heating being turned on.
     
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