timer is off, but still the boiler comes on?

It could be the zone valve sticking open and still calling for heat, but this would mean it's wired direct, not through the timer. Almost certainly an electrical fault as the timer should control all the electrics including the zone valve, pump and boiler. Possibly a timer fault. I have a Potterton Flamingo boiler from about 1979 and it still has the original thermocouple. Try not to be persuaded by salesment to replace it! My Brother used to sell combis to people who had perfectly working conventional boilers - NOT TO ME THOUGH!

Lionel
April 2008