when basin taps turned on upstairs, water comes out of kit mixer below. banging.

[armyash]

As above title.

Customer runs taps upstairs, water starts to come out of kitchen mixer, pipe under sink vibrating.

What could cause this?

 

[gassafe]

Is there a check valve under the sink? Outside tap maybe? They can make funny noises

 

[Chalked]

I've seen this a few times with ceramic disc sink mixers. It seems that when e pressure drops at the tap, the ceramic disc passes slightly.

 

[townfanjon]

Yep odd ball valve does the same

 

[armyash]

check valve is a non return valve correct?

There was iso valves but didn't see nrv's.

I have seen this with ball valves at cast but never seen a tap down stairs affected by running a tap upstairs.