Hot water for washing is too hot (see Extra tip) or too cold.
A problem with a fundamental part of the system. The hot water temperature from the heat exchanger (see main Heating page) is electronically controlled and is pre-set in manufacture. Serious variation in the temperature indicates that something – possibly electronic, but possibly something else in the system – is going wrong.
What you can do
There is nothing you can do yourself. Call in an expert to diagnose and fix it.
See the recommendation re Wapping Plumbing, and warning about non-specialist plumbers, on the main Heating page.
Very hot water is a hazzard and should be attended to as soon as possible because is it easy to knock the shower or handbasin taps and to burn yourself. Burning (‘scalding’) can occur at temperatures above 45° C. At 60°C, second degree burns can occur in three seconds and third degree burns in five seconds.