I have a Towerstat RF thermostat controlling my central heating (about
a year old).

http://www.tfc-group.co.uk/assets/gr...c/STT%20RF.pdf

After the summer (when it never started because the temperature did
not drop), I have now noticed it is not working

The transmitter bit seems to be fine, but the reciever has no light on
it, and reading that doc above suggest it should.
No idea when it failed.

There is an on/off switch on the receiver, but this has no effect. I
have inspected the electrical connections and they are all still fine,
and the boiler itself works fine for hot water, so it is getting
power.

Is there a fuse of some sort inside this receiver unit? Or any other
obvious reason for failure?