To BG MIKE?

sounds like a thermostat problem, it is not shutting off at the right temperature so your overheat kicks in.
cant remember what boiler you said you had

BG MIKE

Glow-Worm Space-Saver 40B MK11.

It ran for 15 hrs overnight (on the very lowest setting) before cutting out. I restarted it again at 07.30 hrs this morning and it is up and running again (still on the very lowest setting).

I didn't think that this particular boiler had an overheat?

Somebody has suggested recalibrating the thermostat (Ranco), is that possible, or am I better fitting a new one?