The four common signs that it's time to replace the nozzle on an oil burner are corrosion, worn parts, clogs and/or warping. The oil furnace nozzle is the feed line end to the fire chamber in the furnace, and if it's clogged, can cause the unit not to turn on.
Since the nozzle is the working end of the burner assembly, it plays a crucial role in making sure a home's heating unit is functioning properly. The nozzle can be easily checked during yearly regular maintenance on the furnace.
Over time, changes in temperature from hot to cold can cause buildup of residue or corrosion of the metal on the oil burner nozzle. This affects efficiency, and if the problem is bad enough, can prevent the furnace from lighting from lack of gas. In addition to the nozzle, make sure the lines themselves are not punctured, worn or corroding, as this also affects gas flow.
Black deposits can gather near the nozzle or other parts and cause clogging of the main line. Keeping the nozzle clean prevents any clogging and eventual corrosion of the nozzle. The metal of your oil furnace nozzle can actually warp over time causing the flow of fuel to become inconsistent or even misdirected. Reference the manufacturer manual before doing any maintenance, replacements or repairs.