Electronic Ignition Furnace Problems
Newer furnaces do not rely on a standing pilot to ignite the gas burners as was the case in older low efficiency furnaces. With a standing pilot (commonly known as the "pilot light") a small gas flame is always burning. The problem with this type of ignition is that it wastes energy by constantly burning fuel and may sometimes fail and go out rendering the furnace inoperable.
With newer mid to high efficiency furnaces electronic ignition occurs in one of two ways:
The intermittent pilot system uses an electronically controlled high voltage electrical spark to ignite the gas pilot and then subsequently the main burners, when the thermostat calls for heat.
The hot surface ignition system uses an electronically controlled resistance heating element not unlike a light bulb filament (and shown in the photo above), to ignite the gas burner.
See the Tutorial Overview and Repair of the Electronic Ignition Furnace for troubleshooting repair tips for electronic ignition furnaces.