Pipes knocking/banging

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Hello

We had a new bathroom fitted before Christmas including a new towel warmer to replace a radiator. When it was done the radiators in the house weren't warming up and the plumber put this down to the ball cock in the tank so he changed it. Before that though he discovered there was an air lock in the system which he drained but that didn't help. The old ball cock worked fine before the new suite was installed but apparently not afterwards? However since then the pipes under the sink or behind the washing machine (next to the sink and this is where it sounds like it's coming from) have been making a quick double knocking noise when the boiler is off or on. Also I have noticed it knocking when the kitchen tap is turned off. It seems to happen less when the heating and hot water is on. I'm wondering whether or not the knocking pipes are down the new ball cock if that's possible. The boiler is a condenser.

Any advice or ideas would be welcome.

Thanks

Phil
 
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From what you're describing, it sounds like water hammer.

When the other chap did the ball valve in the loft, he would have isolated the mains and possibly drained. This could have upset the system in a subtle way. Sometimes the stopcock being on slightly more than previously can do this. I'm not saying he's done anything wrong though...

I would check all the taps and ball valves. It's possible that a washer in one of your other ball valves is to blame. Sometimes if the washer is sticking in a ball valve, it will vibrate as the valve is opened or closed. This can be checked by flushing a loo and waiting whilst it finishes refilling the cistern. The most common time for the hammer is as a ball valve closes. If you find it's one of the ball valves, it's a simple DIY job to replace the washer.

Sometimes it can just be as you open or close a tap.
 
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The old ball cock worked fine before the new suite was installed but apparently not afterwards?
The lights on my car worked fine before you changed my attic light
 
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It's now sorted, it was down to the stop cock. Our plumber popped round to have a look and he turned the stop cock down as well. The pipes are now quiet!

Phil
 
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