Hi, looking for an advice. I've a call in to a plumber but might be sometime before he can get to me.

My central heating has started sticking on full blast. Turned the thermostat off, still on, turned the programmer off and still on. The only way I’ve managed to reset is to turn the mains power off and back on and then all is well for a few hours.
I’m assuming the programmer (timer box) is knackered. Boiler and programmer are two years old

Any ideas.?