Turn the thermostat on the front of the boiler to Off or Zero
Switch off the electrical supply to the boiler - switch it on again
Make sure the timer/programmer is "calling" for heat
Make sure the room stat is calling for heat
Turn up the boiler's thermostat control to mid position 3
Listen for the fan running - does it fire up? If not...
Put in a new question saying what's happening, what's not happening and the specific model of your Potterton boiler - there are dozens of different types - somebody might help you.
Alternatively call in a gas safe registered engineer - use yellow pages or personal recommendation.
Good luck
Peccavi, October 2009
