Thanks for your reply.
The stat generally(!) appears to work as it should - boiler responds by starting up/shutting off as expected.
BUT the reason I'm unconvinced about the stat though is that the first problem I had was that during a heating period the boiler just kept burning whatever I...
Model Drayton (looks like RTS1)
Boiler - ideal Classic LXFF
timer - Drayton Tempus Three
Problem - boiler will not shut down at end of timed period. I've tried all the options on the timer panel, but it seems like it is being by-passed by the stat, eventhough the stat doesn't appear to have...