One thing that can wear out or even get clogged in your heating system is the oil furnace nozzle. This is the actual feed line end to the fire chamber in the furnace, and if clogged can cause the unit not to turn on or heat.
For the most part your oil furnace nozzle is only going to be a focus of importance once or twice a year when you run regular maintenance on your furnace. This nozzle is the working end of your burner assembly and can make or break the way your home heating unit functions and operates.
Over time changes in temperature from hot to cold environment changes near and around your oil furnace nozzle can cause buildup of residue and even corrosion on the metal. This can effect the nozzles efficiency and output as well causing your furnace not to light or not get enough fuel while firing.
Look closely at your oil furnace nozzle using a light and check it for any type of grey or blackish colored build up developing around the nozzle head. You can use a metal brush to remove this from the metal if you are careful to not clog the hole in the process. Most nozzles are simply screw on devices and can be remove quite easily and replaced, be sure not to bend any lines that come to the center where all the lines come together.
Along with the oil furnace nozzle. you want to be sure the lines themselves are not punctured or corroding in any way as this also will effect your fuel intake and cause issue with heating. Other parts that can be worn are the pilot and igniter, these can also get corrosive build up on them, or get old and fail.
Strange black deposits can gather on your oil furnace nozzle and various parts over time and have been known to cause clogging of the main line. Keeping your burner parts clean and free of corrosion and build up can assist in the reliability and stability of your furnace. Replace your nozzle between seasons if possible, or at the least take the time to be sure all these internal components are clean of corrosive buildup.
Warping and Shifting
The metal of your oil furnace nozzle can actually warp over time causing the flow of fuel to become inconsistent or even misdirected. Out side of actual material warping from heating and cooling, parts can also shift in some cases over time so they do not line up properly causing the burner not to operate properly.
If the working ends of the oil furnace nozzle and other lines coming into the burner assembly get bent out of alignment this can also cause issues with the burner lighting correctly. This can happen during maintenance, which could set the pilot out of proper alignment with the rest of the system. There are many makes and models of furnaces and they all have a slightly different burner assembly. Be sure to make reference to your service manual when preparing to make maintenance changes or doing service.