Some service technicians may be surprised to learn that the silicon carbide element of a hot surface igniter (HSI) can be handled without damage. However, it is better and safer to handle the igniter by the ceramic holder. The myth that the silicon carbide tip cannot be handled because body oils cause contamination is untrue.
On a typical heating system with HSI, a call for heat (thermostat contacts closed) will send a 24-V signal to the igniter module. When energized, the module will power up the igniter. If the module is a prepurge model, it will delay 15 or 30 sec before the igniter is activated. On prepurge models, the module will energize the combustion blower or other relays at the beginning of the cycle.