Shower running hot and cold

[gillgilrie]

My parents have Puma Potterton combi boiler and have just had a new shower fitted. It is one that runs off the hot water (not electric). In the middle of showering the water cools right down and then heats up again but becomes too hot. Surely they dont have to keep altering the controls.
What is causing it and how do we rectify it? Thanks

 

[swidders]

Assuming that this loss of hot water doesn't happen at any other tap, it's fair to say that it's a problem with the themostatic shower mixer. Have you any details of make/model etc?

 

[gillgilrie]

The loss of hot water also happens at the bathroom sink, so im sort of guessing it might be a boiler issue, even thought the boiler is reletavily new

 

[bengasman]

The loss of hot water also happens at the bathroom sink, so im sort of guessing it might be a boiler issue, even thought the boiler is reletavily new

a relatively new puma?

anyway, if the problem happens on all the taps, chances are it is a boiler problem.

knowing the boiler i would say diverter is first suspect though it could be pcb, ntc or blockage