Thanks for that - checked the other end of the thermocouple, it is seated firmly and tightened.
The pilot stayed on overnight, and lit the boiler this morning when the timer switch came on, but then went out about half an hour later. Relit it and it has then stayed alight for the last couple...
The pilot light on the boiler, which must be at least 30 years old, did not stay lit. As suggested in other threads I have changed the thermocouple and vacuumed out the burner unit as it was full of crud.
The boiler worked fine for a couple of days, but is now not staying lit. If the...