[SailinAway]

I got the furnace cleaned and serviced today. The cause of the smoke smell was that the flue pipe was a bit corroded. The technician wrapped silver tape around it and said it will last until spring.

Regarding what I was calling a "screen," y'all were right. There was no screen. It was just the clean-out panel on the side of the boiler.

The technician's theory about the short cycling was cold oil or a downdraft during that really cold weather creating a firing delay. The flue is not blocked; draft measured good today.