Air in vented system mystery

Discussion in 'Plumbers' Talk' started by HandyAdam, Sep 10, 2019.

  1. HandyAdam

    HandyAdam New Member

    I have a vented heating and hot water system with a hot water cylinder. The system was drained down so the heat exchanger could be cleaned, but since re-filling there seems to be air getting into the system causing the boiler to make a whining sound and occasionally banging noises. The water heats ok and the heating gets hot. I have tried to bleed the air out from the 2 drain valves near the boiler, and flushing the heating system by opening the drain valve at the lowest point but there seems to be an endless amount of air coming through.

    I've added noise reducer and leak sealer but these don't seem to have had any effect. I have tried putting a cup of water over (or under) the vent that goes into the header tank and it's not pulling in any air from there. I've bled the pump.

    Can anyone give me any ideas where the air could be getting in?
  2. Hans_25

    Hans_25 Screwfix Select

    It could be that there's air in the pipework which can't escape to a higher point and so doesn't come out of any vent. Look for horizontal runs which are not 100% level. Is there noise coming from the pipework anywhere - if so its likely this is where the air is trapped.
  3. HandyAdam

    HandyAdam New Member

    Thanks for the reply. The only place I can hear the noise is inside the boiler or directly around it. The pipework in this house is nearly all under the floors so it's difficult to see. Is there a way to flush the system with mains to push out any possible trapped air? Or a product that can be added to eliminate it I wonder...
  4. Hans_25

    Hans_25 Screwfix Select

    If the noise is inside the boiler, is there pipework at the top of, or above the boiler, that cannot get vented?

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