Thermeco oil fired boiler nightmare?

For over a year we have had issues with a Thermeco oil fired boiler. Repeatedly we have had the jet replaced and commissioned again after we cannot re-start the boiler. The pattern then continues, over a period of about a month the lockout kicks in again, but we are able to re-start the boiler. The operation then gets more inconsistent until after 6-8 weeks from the original ‘fix’ the lock out kicks in and we cannot restart after multiple tries.

We have replaced the oil lines, from the Tiger loop to the boiler. We have replaced the whole burner unit, the solenoid etc. Any thoughts on why the unit is failing – one last gasp try before we put the boiler in a skip!