80s Housing Estate, probably original CH.
The most immediate problem is that the rotating valve that switches
between CH & HW appears to be jamming. I'm surviving by turning it
manually with a coin, and I notice there's an area of increased
resistance at around 2 o'clock on the dial. It's may be relevant that
this is a hard-water area.
The make is Switchmaster; I can't see a model number.
Second problem is immersion heater is dead.
Are either of these fixable by self (some knowledge of plumbing)? Any
advice to give?