Furnace hot surface ignitors
Types of Ignitors
There are two different types of ignitors used for furnaces: the older pilot light systems and the newer electric hot surface ignitors. The pilot light uses a continual connection to the gas used by the furnace itself, while the ignitor needs an electrical current and a filament.
A standing pilot light solves the problem of ignition by always being ignited. These systems use a valve that keeps a constant connection with the source of furnace gas so that the pilot light can always remain in flame, ready to start the main burner whenever necessary. There are two ways the pilot light is kept on. The first is a type of thermocouple system that creates an electrical charge between two metals using the heat of the pilot light, keeping the valve open as long as the light is lit. The second system is called a Milli Volt system and uses the pilot light to power a larger electrical device that in turn operates the main burner, connecting the two even more intrinsically.
The problem with the pilot light system is that it depends entirely on the continuous flame of the pilot light. If the pilot light goes out, the system will not function and you cannot light the main burner. This means that systems with pilot lights need a certain amount of maintenance; in case of malfunction, always check the pilot light first.
Hot Surface Ignitors
The hot surface ignitor system is a more dependable ignition system that works in a manner similar to a heating element or an incandescent light bulb. This electrical system uses a thin wire as the ignitor. The wire possess enough electrical resistance so that when a current passes through it, it generates a large amount of heat. This sudden spark of heat is used to light the main burner. A very high temperature is needed to light the gas, so these electrical ignitors are made out of materials that can both generate and withstand the necessary flash of heat. Silicon carbide is one of the most common materials, a synthesis of silicon and carbon that can quickly become red hot when introduced to an electrical current. These ignitors last from three to five years, while silicone nitride versions last about twice as long.
Hot surface ignitors are more dependable than pilot lights in the short term, but they do burn out like light bulbs and must be replaced occasionally. When using electrical ignitors, always have a spare or two waiting so that they can be switched out when necessary.
How to test a furnace ignitor.