The igniter is what’s going to ignite the gas in the combustion chamber.
Two of the most common igniters are the silicon carbide and silicon nitride.
Silicon carbide is among the older of the hot surface igniters. They come in different styles, and most of them run off 120v. They are very fragile and crack easily if not handled carefully. There’s a myth that the oils in your skin will cause damage. It’s not true.
The silicon carbide igniter lasts typically 3-5 years before failure, and the most common issue would be cracking. You can verify this by reading Ohm’s across the igniter electrical connections, and it would read OL or infinity when cracked. Remember to disconnect any electrical connecting to the igniter, so you’re only reading the igniter.
Silicon nitride igniters are a far superior igniter when compared to the silicon carbide regarding quality and durability. Some packaging will say they last up to 3x the life of a silicon carbide igniter.
DC can power silicon nitride igniters. Usually, around 80VDC and some will run off AC between 24V to 120V.
Honeywell makes a very popular general replacement silicon nitride igniter called the Honeywell Glowfly. It’s a 120VAC (AC voltage) igniter designed to replace over 110 OEM igniters including both silicon nitride igniters and silicon carbide igniters.