I've got a Ferroli combi boiler that is heating the water but not the rads.

if its not calling its the stat or the circuit board, if it is calling but not heating its the valve in the boiler r

If the boiler is otherwise working fine i.e. Hot water normal (not intermittent) It's probably the room stat/ clock If you have trv's , did you shut them all off during the summer? They may need re-opening. Or make sure the pins under the head aren't stuck down, although unlikey on all of the rads I hate to state the obvious but room stat turned up? Clock set correctly and switched to on? Kind regards Terry

Sounds like the diverted valve may be stuck. Properly needs replacing,happens a lot this time of year .