Air in central heating system

Discussion in 'Plumbers' Talk' started by mike21, Jan 4, 2014.

  1. mike21

    mike21 New Member

    I have a Worcester condensing boiler with pump over-run by-pass, a hot water cylinder with make-up tank, radiator valves and separate central heating and water heating valves. There is frequently banging for about five seconds from the pipes in the cylinder cupboard – this occurs whilst the boiler is fired and not just when it shuts down. I have bled all of the radiators several times but no change – presumably there is air in the system somewhere – what can I do/what is the cause.
    terrymac likes this.
  2. BillDL

    BillDL New Member

    If you recently fitted Thermostatic Radiator Valves (TRVs) to any of the radiators, then you can get a similar sound as the water flow starts and stops if a TRV is fitted to the "wrong side". Usually the advice is to fit older unidirectional TRVs only to the flow side, but even bdirectional ones that can be fitted to either side can cause knocking. If you haven't fitted TRVs recently, then ignore this.
  3. mike21

    mike21 New Member

    The valves were fitted with the system about 25 years ago, although at that time there was a conventional Potterton boiler - and no banging - that started when the condensing boiler was fitted and the problem was believed to be the setting of the pump over-run valve, but as the banging occurs when the boiler is fired I had ruled that out - maybe my mistake.
  4. BillDL

    BillDL New Member

    No, you're probably right with that deduction. It was just a thought.
  5. Baxi Boy

    Baxi Boy Member

    You would get the noises if the new boiler is fitted with the flow and return reversed from the original installation and old single direction valves left fitted.

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