Cheers guys I have checked the knob and yes by opening the door. I was thinking it was faulty timer myself but said I’d check with you guys on the off chance it could be fixed without buying a timer which the customer won’t be doing I think. The reason I was called to it was because it was tripping the breaker which turned out to be a broken wire to the heater and this must have damaged the timer.
Thanks again guys
Tom.