Central heating problem - can you please help?

Just back from a weeks holiday, switched heating on but it's not working, water was left to come on for an hour twice a day and there seems to be no problem with that.
For a few weeks, the radiator in bathroom has been warm, even though heating was off.
Any suggestions on how, if at all, I can fix it.
Your help would be much appreciated.
Baxi Solo 2 boiler
Potterton clock
Honeywell thermostat and valve
Many thanks
Rob