how to fix worcester 28 i ?

Hi i had a electrical fault today on my kitchen sockets and the whole board went off when i turned it back on my boiler wouldnt work. I had it serviced last month and the same thing happened when the electrics blew downstairs so the engineer changed the pcb.....

The boiler ignites but goes out after a few seconds but sounds like its still on just no flame.

i have changed the pcb again today and still not working any suggestions? I have bought a flame rectification probe because i got told it could be this , but it looks like a job for an engineer ..... any help or suggestions would be great thanx