"Norbet" wrote

I've just noticed recently that my central heating hasn't been working
- the boiler works for hot water, but although the thermostat
indicates operation it's not actually managing to swicth the boiler
on.

You've tried moving the thermostat close to the receiver and are sure that
the stat is calling for heat?
It is possible that the stat has somehow become "unbound" from the receiver.
These are paired up prior to fitting so that (if you have 2 devices as I
have) the stat talks to the relevant receiver only.
Once you've eliminated all other causes, it might be worth looking at the
stat/receiver instructions and attempting to re-bind them.

Phil