Pipe banging in stud wall

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Manchester
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United Kingdom
We have been in our new house six months with no problems but now whenever any toilet in the house is flushed or any cold tap turned on full a pipe behind the shower in stud wall knocks. It stops when the cistern has filled or tap turned off. There is no water tank and I have tried draining every toilet & tap then refilling the system with no luck. Tried turning down the stop tap a little which cures the knocking but then there isn't enough water pressure. Any ideas?
 
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Normally you can finely tune by turning the mains water stop cock down enough to stop the banging in the wall but leave it open enough for decent pressure.

If that fails to work then clipping the pipes in the wall is the only option.
 
How about a shock arrestor as near to the banging pipe as possible. That must be cheaper and less hassle than opening a wall and redecorating.
 
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Mini-resters work great but are only really needed in very high pressure situations.

As hertsdrainage has said the pipe needs securing to the wall.
 
I see what your saying. But surely restraining the pipe isn't solving the problem. What is the problem in the first place? It's been fine all this time so why would it start now?
 
The problem is that as water flows through the pipe, if the pipe isn't held in place securley then it moves and bangs against whatever is next to it.

If it has only just started then it is possible that the supply pressure to your house has increased recently which might highlight a problem that wasn't noticable before or more likely it wasn't securely properyl in the first place and has worked loose.

I had this extact problem when I re-did my bathroom, I didn't secure the hot feed properly and it banged like crazy, so much that eventually it burst the compression fitting. I secure with some additional clips and it was all hunky doray after that.
 
If the problem has just started It may be worth your while contacting the water company and asking if the pressure has increased. If it has then it may be less a hassle to fit is pressure reducer on the mains pipe. If ripping out a wall and redecorating is more hassle then the pressure reducer may be the best way. When you decorate the pipe can be clipped and the pressure increased at the valve.
 
You said, "We have been in our new house six months with no problems" - if you *mean* "new", get the builder back to sort it!

Here's an option -
Instead of opening up the wall to fix new clips, just drill a small hole or two as close as you can to the trouble (without puncturing the pipe!), and inject foam.

What do others think ?
 
Update.

Made a hole under the bath to expose pvc pipes to the mixer shower. It feels like the banging is comming from inside the mixer. If I turn the shower on the banging stops. I'm guessing I need to change the seal inside the mixer? Would it be the outlet seal or is there a seal within the temperature mixer?
 
Update.

Made a hole under the bath to expose pvc pipes to the mixer shower. It feels like the banging is comming from inside the mixer. If I turn the shower on the banging stops. I'm guessing I need to change the seal inside the mixer? Would it be the outlet seal or is there a seal within the temperature mixer?

It's stopped because the water pressure is lower, because the shower is on. Also, the shock waves have a release through the shower. If you're convinced it's the shower, and it's an exposed type valve, remove the mixer, plug the open pipes and see if the banging has stopped.

You could try one shock arrestor, but these really need to be close to the toilets or taps that make the banging happen. Put one arrestor near a tap. If using that tap no longer causes banging, then fit arrestors near the other taps and toilets.
 

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