Ok, really really strange... CH now works, but don't know why...
After sending the kids to bed with hot water bottles last night, I turned the boiler off overnight.
This morning turned it back on and it was exactly the same... HW, but no CH, even though the controls were demanding it
The HW light was permanently 'ON' on the front of the boiler, but the CH light didn't light up. The boiler seemed to be running and firing up every few minutes, with the temperature lights gradually increasing before it cut out. (pre-heat is turned right down).
I then turned the hot tap on in the kitchen where the water came out hotter than 'normal'. Oh well I thought, time to call a plumber. Went back to the boiler and low and behold, HW light was now out, CH light was ON, boiler firing and radiators getting hot.
Fantastic, but something has caused this to happen and I guess will need replacing / cleaning. Any ideas what could have stuck here so I can prevent it reoccuring?
Thanks in advance.