My Glow Worm Micron 30FF wont light. How can I check whats wrong&fix it?

I have a Glow worm Micron 30FF which was installed new 4 years ago. Since then it has been serviced and a new pcb was installed last year. It has always been a bit temperamental but for the last few days the boiler wont light so theres no hot water or heating. Ive tried the fault finding info in my manual and it looks like a pcb issue again. There are 2 led displays - one for reset which lights as it should and one for the burner which mostly wont light but will occasionally light for about a minute before cutting out again. The pipes leading to-from the boiler are cold other than one which is very hot. Im wondering if it might be to do with overheating. Any ideas very welcome. Thanks x