BAXI SOLO PF 40 - knocking/clicking noise?

Hi there hope someone can diagnose my problem!

the heating/hot water will come on for around 20-30 mins and be fine then all of a sudden there will be a clicking noise from the boiler a mild banging or so.. then the pilot light will go out and not come on ive read many things it could be... pump, pcb, pilot ignitor.
Just wondering if anyone knows what this might be.
I am scared of teh price if I call out an engineer.. what could I expect or could this b a simple fix?