One for the plumbers... Why are my pipes bangin' ?


a short-tempered ill-controlled small-minded troll
The water pipes in my house have been bangin like crazy over the last few months... so after a bit of Googling, i turned off the mains, opened the highest tap*, opened the lowest tap and drained the system, closed the taps and turned the mains back on. And it worked... for a few days.

Before my attempt at a remedy, it seemed like any tap on any floor could trigger the water hammer... now it seems like just the ground floor taps. A new kitchen and bathroom has recently been fitted in the downstairs flat, and the water hammer has got much worse since.

I've lived here sicne 2002 and there's always been some bangin', but it seems to be getting more and more frequent.

*actually, it was 2nd highest, the guy in the upstairs flat was out.

any ideas how i can remedy it, or at least suss out the cause... or is it just old/shoddy plumbing?


Quite dreadful
lost somewhere
It's often a dodgy float valve in a WC cistern or the cold water tank. If they shut off too suddenly they set up a hydraulic shock wave. See if the hammer happens just after the loo is flushed. If it doesn't, see if the ball valve in the loft is to blame.
Also check if your WC is leaking flush water into the pan slightly - might happen if you have one of the valve type flush mechanisms rather than the syphon type. Cistern drains down a bit via leaky valve, float valve then refills cistern then causes the banging when it shuts off. Repeat continuously.


a short-tempered ill-controlled small-minded troll
After draining the system, i only turned the stop cock on 'a bit'... in fact i haven't asked my upstairs neighbour if he's getting a trickle or a flow.

As far as I know, flushing the loo doesn't trigger it... does that mean i can dismiss the ball valve in the loo?


Legendary Member
I had that once, it ended up being a leaky tap washer.
It's called 'water hammer' and it's caused by a resonant frequency in the pipework. In a pressurised system it can be caused by a loose valve washer, by pipes with too few clips (1 metre us the maximum recommended spacing on 15mm pipe for example). Or a combination of both. I've seen ball clocks literally bouncing up and down on the water surface in a toilet cistern. Fixed by adjusting the water's depth.

Often it's enough to change the washer or simply disturb it by turning it on its seat.

We get water hammer in our Ch circuit at work. It's starts off quietly and gets louder over a period of time, so it sneaks up on us. Just turning any one of the thermostatic valves a tiny bit is enough to stop it.

If clipping your pipes and furtling your valves doesn't work you could try turning down the flow in the appliances isolation valve.

That'll be £245.00 please madam.


Über Member
When you did a partial drain and refill you put an air bubble in the pipe run that acted as a shock absorber, the upstairs neighbour has now rather unhelpfully bled this out - so you need another - or fit a shock arrestor which is nothing more than a teed joint on a horizontal run with the closed branch trapping an air bubble to absorb sudden valve closures from rattling the (undoubtedly) loose piping downstairs.


I've put up with banging pipes for 5 years. Couldn't figure it out.

Recently when the toilet is flushed, if the cold water tap in the bathroom sink not tightly closed, it starts gushing water.

Any ideas? Is it the Cistern issue mentioned above?
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