Problem with 24kw Baxi Potterton Main System 24 HE Boiler?

make sure you have the correct water pressure for the boiler which should be between one and a half or two bar. if it doesn't light up then and keep running. Check if the pump is working and circulating the water. take a screwdriver and put one end on the pump and the other end to your ear, and turn the boiler on. You should hear the pump turning. Any thing else than those two faults, and you need an engineer to check it out. Could be other faults causing this such as a faulty thermistor or a domestic flow valve.