The heating select button does not move the arrow from off, hot water select button works ok

Neil, October 2022

I wonder if it's a stuck or failed diverter valve. There could be a manual lever on the diverter valve that you can move and latch in place. If that turns the heating on, it could be that the diverter valve motor bit needs replacing, rather than the entire valve.
You'll need to do a bit of sleuthing and browsing to understand more.

Fghi, October 2022