Water pipe knocking when hot water comes on

Discussion in 'Plumbing and Central Heating' started by blueagle78, 16 Oct 2008.

  1. blueagle78

    blueagle78

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    I've been searching this forum but couldn't seem to find the answer to my problem hence posting this thread.
    I refurbished my house recently and the hot water tank which was downstairs was moved in the loft by a plumber. It sits just underneath the cold water tank. The hot water is set on timer so boiler heats up the water only once in a day. Knocking/banging sound is coming up every time boiler starts heating up the water. It goes on for about 5 to 10 minutes and then everything goes to norm. This is happening only when the hot water is coming on and not with the central heating.
    I hope you guys would be able to suggest something and I'm sorry if I've posted a question which have been answered in the past.
     
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  3. Jimmyjammy

    Jimmyjammy

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    Have exactly the same probelm. Its air trapped in the pipes. Also sometimes it can mean there's some rust in there. As there can be sediment that builds up in the pipes causing more pressure. Hence the pipes expand and contract and you hear the banging and clanging.

    I've heard you can get you pipes cleaned with a high pressure water / chemical mix. It costs about £270 and takes between 3-7 hours to do. Not sure to be honest. But That banging is damn annoying! :eek:
     
  4. seco services

    seco services

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    shouldn't be any air trapped in the system. unless its drawing it in the vent pipe.
    and powerflushing is not done under high pressure.
     
  5. blueagle78

    blueagle78

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    As I've set the timing for hot water, it comes on at 6am and within minutes the banging sound starts. Its a single bang sound with a delay of few seconds and it carries on for about 5 minutes. Then everything is back to normal. I just hope someone would suggest something to try here because its just really annoying because we need hot water in the morning and this banging sound always wakes me up way before I need to be woken up.
     
  6. seco services

    seco services

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    have you checked all the pipes to the cylinder that one isn't banging on exspansion when first heating up.
     
  7. blueagle78

    blueagle78

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    Thanks for your response. The problem is all pipes from upstairs to the downstairs where the boiler is are behind boxes so I don't have access to them. But I can see them all in the loft. I've this feeling its expansion banging but how could I confirm and rectify it?
     
  8. Stephen19

    Stephen19

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    Why not delay the hot water coming on until you need to wake up. Then you get a double whammy, a "hot water alarm system combo"...do away with the pesky radio buzzer alarm on bedside table and you have more room for lots of other trash!
     
  9. DIYnot Local

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    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

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