A pilot light on a furnace can sometimes go out for no reason at all, and oftentimes all you must do is reignite the pilot light to get the furnace running again. Most furnaces with an electronic ignitor switch operate much the same way. Usually there is a selector on the furnace that has a setting called "Pilot," which is used to re-light the pilot. Lighting the pilot should only take a few minutes even for the novice.
Shut off the gas supply to the furnace, and wait 20 minutes before attempting to light the furnace. If the furnace has a switch on it to shut off the gas, use it; otherwise you must shut off the gas from the closest shutoff on the gas line running to the furnace.
Turn the selector on the furnace to the "Pilot" position; on some models it may be labeled as "Light."
Turn on the gas supply to the furnace.
Press the ignitor switch while holding down the pilot ignitor button. It may take several attempts to get the pilot lit.
Turn the selector to the normal operating position, which is usually labeled "Heat."