Hot surface ignitors are use in many gas furnace applications to ignite the main burners. The ignitor will receive power after the draft inducer has been operating and cleared the heat exchanger of any leftover gases. It should glow bright orange. The gas valve will open once the ignitor has been powered long enough to reach proper temperature for ignition. The gas should light immediately. The flame will travel across the burners and reach the flame sensor on the opposite side of the burners. If the flame does not reach the flame sensor the gas valve will shut down and the process of the draft inducer clearing the heat exchanger of leftover gasses will begin again. The furnace will attempt to light 3 times and then will lock out and need to be reset by shutting off power and restoring power with the power switch. You will need a volt meter to check the ignitor. Shut off power and connect the probes on the volt meter to the 2 leads of the ignitor. Make sure the volt meter is set to read AC power. Turn power back on and watch the volt meter. If the ignitor does not glow while the power is applied the ignitor has failed. If power is never applied you may have a bad circuit board.
This is a very common failure item and should be kept as a spare. It is quite simple to change. The only tools needed are a 1/4" nut driver. Extended length with magnetic tip makes the job easier. Common cause of failure is insufficient air flow such as dirty filter or restricted ducts. Make sure registers are open and returns are not blocked and evaporator coil and blower wheel are clean. Air flow will cause the burners to cycle on limit switch. Switch may trip 8 or 10 times during a heating cycle causing ignitor to repeatedly heat up and cool down.