The Silicon Carbide igniter that has been used by furnace manufacturers for a long time is old technology that hasn’t changed much in almost 60 years. They are very fragile and will break very easily. Grease or dirt can cause premature failure. They are available with different ceramic bases but most of the silicon carbide elements are the same and one thing they all have in common is that they fail more than any other part of the furnace.
Exact replacements from the OEM are thought to be the easiest way to replace these SC igniters. With the same base and same plug as the original, they will fit easily and quickly into the furnace requiring no retrofitting. Caution should be taken with any SC igniter not to bump the element or to touch it with your fingers. The grease from your fingers can cause premature failure. Some manufacturers suggest that you check the resistance with an Ohm meter after installation to ensure the element is good. They recommend a resistance of 50 to 90 Ohms for the flat style element SC igniters.
The newer Silicon Nitride igniters are much more durable and are much tougher to break. They are easy to recognize by their smooth non-porous surface. They also use less energy to operate than the old SC igniters and they will normally outlast the SC igniters by 2 -7 times. Many OEMs are switching to SN igniters in their new furnaces and some offer retrofit kits. The SN igniters may cost more but they will outlast the SC igniters and are a great upsell. The benefit to your customer is a much more reliable igniter and less downtime as one universal SN igniter carried on your truck will replace hundreds of OEM igniters. Universal SN igniters may look different, but retrofitting is quick and easy as the universal SN igniters will come with multiple brackets to fit the original mount in the furnace. OEM may not always be the best choice when it comes to igniters. Because of the durability of the SN igniters even in warranty igniters may be a place to upgrade to SN igniters. Always refer to igniter manufacturer's cross reference before retrofitting. In some applications, the SN igniter may not work such as in a furnace that doesn’t utilize a flame sensor.
Don’t forget to clean the flame sensor when changing the igniter. The sensor conducts a very small current so a small amount of oxidation may prevent the current from passing causing annoying lock-outs. Make sure the ceramic and rod are in good condition and clean the rod with very fine steel wool.