[Richard]

Here is another scenario that requires investigation.

You have clearly said, you hear it giving out and relighting. It can and will do that, the brain does not immediately shut the unit down if the flame sensor does not produce the correct resistance. The brain will fire the coil a couple of times before it shuts down.

You have to listen carefully to the “roar” to see if this is happening. If the roar disappears and almost instantly resumes, the unit is relighting. This is a tough problem to definitively diagnose.

First things first, have you cleaned the combustion chamber and installed a new nozzle ? That is not the same as I put a new one in some months ago, and it hasn’t run on diesel. Small drops of diesel harden on the nozzle when the unit is run on electric for long periods and no diesel use