pipes knocking with combi boiler

Discussion in 'Plumbers' Talk' started by Cityneil, Jan 3, 2005.

  1. Cityneil

    Cityneil New Member

    We have had a combi bolier isntalled and we get a fair bit of nose from (I assume)the pipes 'knocking' or 'banging'.

    Is this just an air pocket so rads need to be bled? Or is it something else?
     
  2. John.R

    John.R New Member

    I assume the system has been fitted with thermostatic radiator valves (TRVs).

    Most TRVs can be fitted in flow or return to the rads but they have to be turned around if fitted in the return pipe. When the TRV is closing down they can hammer if in the return pipe.
    Some TRV's it does not matter but they are rare.
    I would have assumed the installer would have checked before final fix.
    If this is the problem no solution but to have the TRVs turned or placed on the other end of the radiator.
     
  3. Cityneil

    Cityneil New Member

    John, thanks, will check. Assuming all ok on TRVs should bleeding the rads help? Or do I have to find knocking pipes and fix in place?
     
  4. John.R

    John.R New Member

    If the system is a complete new C/Heating system. Then I agree it maybe
    loose pipes touching and vibrating
    Could be tight pipes expanding in joists, but that would stop once hot and only occur again when going cold.

    Bleeding. New system water will have air in the water. This will separate from the water and cause bubbles which will enter rads. Bleeding will get ride of the air. Watch the pressure drop. You might have to give small refill.
    I would not say the sound of bubbles is a knocking or would cause a knocking sound.

    TRV's. How best to check. When knocking occurs turn all TRV's to max heat. If this stops the knocking then you are safe to say its one or more TRV that's causing the noise.
    In any new installation you must have one rad that is not a TRV this should be where the room stat is. Otherwise when all TRV's turn off the system can't cycle the water. Some boilers can accommodate this but not advisable in any situation.
     
  5. Cityneil

    Cityneil New Member

    John

    Think I will try bleeding, boiler and a couple of rads new but pipework and rads upstairs old. Noise occurs when starting up and continues as long as heating is on - driving me nuts!
     
  6. amo gas

    amo gas New Member

    could be trvs pipes but very possible cold main not secured don't be tight call a corgi reg engineer you know it makes sense
     
  7. maxply45

    maxply45 New Member

    get a corgi to fix a loose pipe ?

    What's next get a sparkie to change a light bulb ?
     

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