Nozzle Trash
It was getting cold when the furnace quit, so we decided to do some fuel oil furnace troubleshooting before calling a repairman to come out. The burner was running but there was no fire which could be caused by a number of things. My wife suggested that the electrode wires had shorted out or were just dirty. Fortunately I found the problem in the burner nozzle. Since the opening is smaller than the tip of a pin, even a miniscule piece of trash can clog it up. It is a cheap part to replace, and now the furnace works great.
