Many older gas furnaces are ignited with a pilot light (most newer models use an electronic ignition for better efficiency), and occasionally, that pilot light goes out.
Pilot lights can go out for a number of reasons; some of the most common causes include:
A blocked valve – A buildup of dust or debris can cut off oxygen to the pilot light’s intake valve, making it difficult for its flame to “breathe.”
A malfunctioning thermocouple – A thermocouple is an electrical switch that varies its output when temperatures change – on your gas furnace, it’s used to cut off gas supply as a safety measure. If your pilot light has gone out, your thermocouple could be damaged; if it is, contact a qualified heating technician (replacing a thermocouple is definitely NOT a DIY job!).
A fuel leak – If there’s not enough fuel reaching your pilot light, it could blow out or glow yellow rather than blue: this typically indicates a fuel leak somewhere in your system. Your furnace responds to that leak by automatically shutting down for safety reasons. If you see a yellow pilot flame, contact a heating pro right away.
Wind or drafts – Most pilot lights simply blow out. Luckily, this is one of the easiest problems to fix. Follow these steps to reset your pilot light:
Step 1: Always follow manufacturer’s instructions first (see the side of your furnace unit or your owner’s manual for details).
Step 2: Find the gas valve in the pilot light assembly; it typically has “on,” “off,” and “pilot” settings.
Step 3: Turn the valve to the OFF position and wait three minutes or more for It to reset.
Step 4: After three minutes, turn the valve to the PILOT setting and hold a lighted match next to (not inside!) the pilot light opening. While holding the match, push and hold the reset button on the pilot control panel until you see the pilot light ignite, then set the valve to the ON position.