Last week I did the annual service on my Beckett burner. Cleaned and vaccuumed the heat exchanger, checked for cracks, replaced filter, nozzle, set the gap, etc. Started it, bled the air twice, ran fine.
Tonight, I turned on the heat and it tripped out. I reset it, looked at the flame. It seemed weak, and the stack was belching very thick white smoke. It tripped out again. I thought about bleeding air again, but something seems wrong. Could it be water in the line? Tank is full and never runs dry.
I'm a stationary engineer and work on some small burners at work, but just know the basics of these. I know it's time to call a pro, but what can I check for myself? Thanks

The oil delivery system seems OK since you got white smoke (not a good situation actually)

Your ignition is not working.

Transformer,electrodes etc is where the problem is at.

Check the gap on the electrodes and the transformer discharge voltage. Also check for cracks on the electrode insulators.