ideal isar he30 boiler?

I have an ideal isar he30 combi boiler. My problem is that the central heating is'nt coming on but the hot water is working fine. I have had the system fitted for about 4 years and last year had to fit a new (Orange) upgraded pcb as the boiler was not working at all. This year when i came to use the central heating side of the boiler it just would'nt kick into life apart from randomly a few times in the last week. The boiler receives a signal from my wireless unit telling it to come on but nothing. any advice is appreciated thanks

have you a multimeter?

when you say it comes on.. is it only for a few seconds? possible thermistor..

Last night i turned the boiler off for a minute at the main switch. When i turned it back on it worked and warmed the house up but now its not working again. When the drayton wireless unit sends the signal to turn on the fixed drayton unit recieves the signal the red light flashes then the top light goes green which sends a signal to the timer and turns a red light on which should turn on the boiler but nothing now

Turn of mains power to boiler remove 5 pin black plug and the centre bottom of boiler, hold it with the pins towards you and reading from right you should have Live, neutral and earth, and then 1 or 2 other wires on the left.
put a link between these two other wires as this is how it comes out the factory (marked L1 and L2). this will do away with your external controls.
If the heating comes on now then its faulty external controls if not it mat be the front user controls potentiometer reading low 32 degrees.
Also a dripping tap with cycle the boiler to hot water not allowing the ch to come on