Off peak hot water has stopped working on a BP 220

Hi

I have an 8 year old Pulsacoil BP 220.

It has stoped heating up with the off peak timer.  The boost button still heats water day and night.
I suspect the off peak heater has stoped working.

I have no experience of hot water heaters etc. so expect I'll need to get a professional to come to replace it, but any advice or observations so that I get the right/best person along (or even solve it myself if possible) gratefully received!

Cheers

Tim

Turns out the off peak thermostat had burnt out. Maybe caused by a loose wire.

30 mins to diagnose and replace.