I couldn’t override the old controller. Something was jammed or broken inside. So to put the heating on, I had to turn the dial so the programme and time were out of sync. Horrible design, rubbish construction.

I took the opportunity to buy an electronic timer that reinstated the functions of a Honeywell timer from the 1980s!

Cover removed from boiler showing manual controller.

Old controller just slid up when boiler casing removed .
New electronic controller
 
New controller in place, working well.