I have fitted a thermostatic shower mixer. However when the water is turned on the overflow continually discharges water. Is it because the cold water pressure is so high that it flows through the hot water? Will a non-return valve in the hot water cure the problem?

ian dal, May 2009

I have had the same annoying problem & have been told that the cold feed should not come from the mains but from the header tank. How does this work cus no plumber I know can figure it out!!

Also thinking of giving the non return valve a try. Are they really 30 odd quid??

Apparently these should be fitted regardless of cold mains/tank feed due to water regulations. Funny it dosnt say this in the instructions.

Nelly, June 2009

but thats not your main problem it sounds like u have tank fed hot & mains pressure cold in which case u should have got a pressure balancing shower valve & not many co do a thermostatic pressure bal valve, a normal thermo valve will only control temp not pressure, u really need hot & cold supplies at the same pressure, by fitting a non-return valve in the hot will stop the tank from filling up but because they contain a spring this will mean that it could reduce the hot water flow rate & because cold will be pressing on the other side of the valve it may stop the valve from opening at all which would mean no hot water coming through at all, if this is the case & it's not possible to change the cold supply to tank fed then u could either change the shower valve or fitting a shower pump to the hot supply to the shower would prob work.
hope this helps.

Keith Gillyon Plumbing, Heating & Building Services (southampton), May 2009

should do

Mr K, May 2009