Knocking after replacing filling valve in toilet Drainage and wastage systems and plumbing help, advice and answers

[Eva Kay]

have replaced the filling valve in the cistern of my upstairs toilet. It is working fine but now every time someone sits on the seat the pipes make a fairly loud 'knocking' sound. I followed the installation instructions to the letter, have fiddled with height of valve, water feed tap and tightening of back nut all to no avail!

[htg engineer]

I can't see the knocking having anything to do with people sitting on the toilet, unless you have taken clips off the pipe and not replaced them. Even then if the toilet is secure it shoudln't happen.

They sometimes bang when the cistern has filled and the valve closes, this is normally caused by the pressure to the valve been to much, or as i said before pipes being inadequately clipped.

Trying turn the isolation valve off slightly if it has one, if not close the mains cold water stop tap a few turns and see if it stops.