Unexplained pipe clunk

Water hammer can easily be transmitted from neighbouring properties.

You can fit an arrestor just after your stopcock, it may reduce it, rather than stop it entirely.

Heating pipes cooling/heating and sliding in a clip?

Is the water supply to the loo incoming mains or maybe from a tank? If a tank could it be when the float/ball valve finally closes after what may be a slow fill towards the end as the valve gradually closes down.

Washing machine running and water fill stopping?

If a tank is feeding hot water - hot water leaking/dripping and periodically the tank needs to top up and the clunk is the ball/float valve closing.

We had something like this a few years ago. I eventually traced it to the loft cold water tank float valve. Trying to fix it caused more problems than the original fault. A new washer, and then a completely new valve introduced severe water hammer and even a "foghorn" effect! The *only* cure that worked to stop this was to partially close the isolation valve on the water tank input.

To the best of my knowledge downstairs 2 sinks/loo/boiler, upstairs 1 sink and a loo. Clunking while nothing in use.

So unless something else is piped up... but i'm near 100% sure not.

Handy to know, ta.

What kind of hot water system?

Yes but just one clunk. I used to get that on my old washing machine when the solenoid valve closed, despite it having a flexible poipe. I reduced the water flow a bit with the stopcock and it went away. Brian

"Brian Gaff \(Sofa\)" snipped-for-privacy@blueyonder.co.uk> wrote in news:rua5pm$4i9$ snipped-for-privacy@dont-email.me:

Brian - possibly the hose is too flexible. I get it if I leave my garden hose turned on - with the nozzle turned off. It creates a superb rebound device when a tap is closed.

Sometimes un-anchored, hidden pipes will try to straighten when the water pressure is suddenly raised (when turning off a tap), this causes physical movement of the pipes.

Combi boiler.

Pretty sure it's nothing to do with that, it's in the same room and was by all accounts inactive at the time.

Yup, probably not that...

I have noticed with my unvented system that if you leave a tap dribbling, you can get the occasional clunk as the system accommodates the slight pressure variations. (interaction with the pressure reduction valve and the expansion vessel probably).

Does your system have any PRVs? (including things like a pressure balanced shower)

If there is a length of plastic soil pipe fixed along a surface, that can also clunk when you feed hot water through it causing it to expand.

I find that reverberates in a certain way, it has that dull plastic sound.

I've also heard of a rain water gulley letting go after a change in temperature that was a bit louder than the average pipe noise!

I'm not sure if the OP will find the noise source unless he can reproduce the noise manually.