I'm experiencing burner lockouts on a Wallstar 15/20 oil boiler. Lockouts are Intermittent, replacement control box, solenoid coil and photocell have not fixed the problem. When attempting to reset the lockout it goes through the ignition process and I can smell oil so I'm assuming that oil is present but ignition is not taking place. I have to wait about 15 minutes (cooling down?) before it will fire up. Any ideas what else to look at?

Ignition transformer test for high voltage rate over sustained operation.

Thanks for that. The Engineer looking at my boiler is returning after Christmas when I'll pass on your suggestion. Until then I foresee several lockouts! Happy Christmas.

The reason I mentioned the high voltage ignition transformer is the fact that they can work well then drop out then start working again plus the fact that you have replaced most of the other parts. Merry Christmas.