Glowworm Ultimate 40FF?

DHW working fine and all neons come on in correct sequence. For CH, Neons 1&2 keep flashing, fan runs for about 5 seconds, boiler tries to ignite then nothing. CORGI Reg guy carried out power flush, then changed divertor valve and then the pump, but still no CH. I could have had a new boiler installed for money I have already paid out. I now suspect the PCB, but all is fine for DHW. Any ideas anyone.