Now an admission: I made a post on this yesterday, but I think it was
over specific in terms of detailing the manufacturer (Sime) etc. What
I'm looking for now is just some general guidance on how these things
work, as I'll probably get someone out to do it, and I don't want to get
stung. I just spoke to a guy who was very vague, talking about some
piece of kit between the power and the clock, which could go wrong.

Set the timer to be on 24 hours a day. Replace your room thermostat with a
programmable type. Then it doesn't matter that your clock is knackered, and
you have the heating controls in the lounge, where they belong and all the
advantages of a programmable thermostat, such as selecting a specific
temperatures for different times of day.

This presumes that the same fault doesn't prevent the 24h option from
working.

Christian.