Thanks chaps, i sorted it out by switching the tap of the hot water pipe coming into the shower off then turrning it on only about about half a spin, so there's less hot water combining with the cold one. It'll go it for now. In the winder I'll open the tap more.
The water temperature of my power shower is becoming increasingly high as the weather warms up - it must be to do with the cold water tank in the loft becoming warmer. So much so that in the summer it is almost too hot to take a shower even with the temperature knob turned to the minimum. Is...