Clonking in pipes when turning taps off

[Zippee]

Since yesterday we have been getting a single clonk in the pipes whenever we either shut taps off, the washing machine or dishwasher finish pulling water in or a toilet cistern is full. In the kitchen you can feel the tap jolt slightly with the force of the clunk. This happens regardless of whether its a hot or cold tap (combi boiler if that makes any difference).
I've checked theres nothing pressing on the pipes, the boiler is at normal pressure etc but have no idea what is causing it and it's driving me mad. Any ideas what it could be?

[Ronstein]

Could be as simple as a broken pipe clip somewhere

[Starfighter]

Water hammer. The sudden shut off of flow causes a shock wave through the water. Any longer the SR pipes will move and create the bang. You can get fittings like a shock absorber that will eliminate this.

https://youtu.be/FbkE0HhEHVY

[Lincsls1]

It is called water hammer.
As above, could be a broken pipe clip somewhere.
It could also be due to a rise in mains water pressure increasing the water hammer effect. Have the local water board been working on the supply recently?
Turning off your taps very nicely should stop them making the noise but obviously you can't control the other stuff.
It will NOT be anything to do with your combi boiler.

[Lincsls1]

Starfighter said:

Water hammer. The sudden shut off of flow causes a shock wave through the water. Any longer the SR pipes will move and create the bang. You can get fittings like a shock absorber that will eliminate this.

https://youtu.be/FbkE0HhEHVY

I would think a small expansion vessel fitted to the mains would also do the trick as the air/diaphragm in the vessel would probably absorb the shock.

[Zippee]

Thanks all.
No rise in pressure from what I can tell. I'll have a root around and check clips but I couldn't see abutting on initial inspection. The fact it only started yesterday hopefully means it's an external pressure thing then

[Ynox]

I had similar with my toilets when I moved from a gravity fed system to mains pressured.

Sorted it by fitting hammer arrestors inline into the supply for the toilets. They work well if kind of expensive for what they are.

[neil-c]

You haven’t had the water shut off at all recently? We had this after a new bathroom was fitted and it turned out the main supply valve had not been reopened fully.

[Zippee]

neil-c said:

You haven’t had the water shut off at all recently? We had this after a new bathroom was fitted and it turned out the main supply valve had not been reopened fully.

No, nothing changed at all. Just started a couple of days ago. Had a look and can't see any broken clips on the visible pipes.

[Sheepshanks]

neil-c said:

You haven’t had the water shut off at all recently? We had this after a new bathroom was fitted and it turned out the main supply valve had not been reopened fully.

That's a surprise - you'd expect it the other way around.

[Scabutz]

We have really high water pressure and a megaflow system so hot water comes out at the same pressure. We get massive water hammer. When I re did our en suite I used those shock absorbers and they work really well. In the US they install extra length of pip capped off past the fitting but I think that is no allowed under UK building regs.

It has got worse over the years as once one clip comes lose or fails it will eventually start snapping multiple clips.

[Gingerbread Man]

Water hammer gets worse with higher pressure. Higher pressure water suddenly having nowhere to go when an outlet is shut off. What is your household pressure? Too high and product warranties might not be upheld anyhow.

Often caused by washing machine/ dishwashers or toilets shutting off due to the sudden stop of those type of valves. Also these type of fixtures often have isolation taps that are left on as the end valve does the on and off itself. The open valves washer can bang as they jolt.

Can be an unclipped pipe causing a pipe to move. Can be a non return valve.

So check the pressure. Reduce with a valve after your internal isolation if high.
See if you can reproduce the knock. Then turn off all isolation valves that feed washing machines, dishwashers and toilets. Does it still happen? Isolate the combi (hot). Try locate the source. Try again.