I had a new concealed cistern fitted by a plumber a few weeks ago. When flushed the cistern refills at high speed and the fill ends with a sort of banging sound which is presumably the valve closing. I'm not sure whether this is normal or not or whether something is wrong. Any thoughts?
Could be that a low pressure nozzle is fitted in the cistern valve or a flow restrictor for high pressure has been omitted. The inlet pipe into the cistern should have an isolating valve fitted try closing this so the slot is at 45 degrees and flush the cistern again, gradually close it more and see is this eliminates the problem.