[mickinuk]

Mike,

Your burner needs servicing.  Cleaning and a new nozzle will solve your issue.

Allowing the burner to sit not used following burner service allows the diesel on the new nozzle to congeal ruining the fine mist spray pattern.  This results in some fuel not burning causing white smoke.

Once you service the burner, run it once per month through one heating cycle, period.  The burner can go 1, 2, maybe 3 years before needing service again.

A burner that is not seated properly will produce lots of black smoke.  Black smoke is more fuel than air due to combustion air leaks around the poorly seated burner.

Hope this helps.

The nozzle was only 1 month old from service. I believe the fault was a burner that was not fully seated. A consequence of this is that the combustion chamber melted. I don't know if you have seen such a thing before. See attached photo's, the one with text is looking down the tube into the combustion chamber, its a bit blue looking because of the LED light I used to illuminate the photo.