ya after i signed up i noticed this is a site based in the UK.
I never ran across this problem before. I'm an "apprentice plumber" here in the states I have limited experience in service work ect. I usually build commercial building.
Your Pipe hangers ,strapping,supports are not installed correctly, There is usualy a standard to go by with your local city codes.
If you are working with copper every 6-8 feet the pipe should be supported.
If working in plastic of any kind . pvc cpvc , Pex 3-4 foot. That is usually what...
In the shower the hot water side has very little pressure. I took the shower faucet apart . Feeding the hot water side there was a piece of plastic blocking the small hole. Attempted to remove it. It broke off.
So i had to get into the wall. Broke 2 tiles out. Turned off the water...