Water not getting fully hot

Lorian

Also....
Is your flow temperature high enough - not reduced it recently to save money?

In your programme try making the hot water  heated when the CH is not on.

Interesting pipework, but all the copper around the tank could do with lagging. Looks tricky though. The gaps in the tank jacket need closing/taping, to avoid losses.

Ectophile

Another possibility, if you're in a hard water area, is that the heat exchanger coil in the hot water cylinder has furred up.  This makes it harder for the heat to transfer into the tank.

This is only likely for an old tank in a hard water area.