Shower running hot and cold with no loss of power

[gazi]

Hi, What can i do to get a hot shower again.
We have a worcester 28cdi combi bolier which is about 8 yrs old and we have a Bristan Power Shower which is about 8yrs old. When you run the hot tap it stays hot and the boiler is fired up all the time. When we have a shower it keeps going hot and cold with no loss of water power and the boiler still is fired up all the time.We have a dial on the boiler that has a grey and red hand on it. The red is on the 1 and the grey is between 0 and 1. thanks

 

[Youllneverguess]

Is the shower thermostatic?

Could be its cartridge.

Alternatively you might need a new plate heat exchanger.