A pilot light on your furnace is a small open flame that is fed by a steady flow of gas used to ignite the gas that heats your home. Problems can occur when the gas flow is obstructed or misdirected, or when the pilot light is blown out. In newer appliances a safety device called a thermocouple, which is a heat sensor that turns the gas off if the pilot flame is ever extinguished, accompanies the pilot light.
How should the flame appear?
A correctly adjusted pilot flame is steady and blue, and stands between 1/4 and 1/2 inch tall. If the flame continually goes out, it may be getting too little air; if it's yellow at the tip, it's getting too much air. To correct either problem, turn the pilot adjustment screw slightly, as directed by the manufacturer.
What do I do if the pilot light goes out?
Re-igniting pilot light is not a difficult task. If there is a gas valve at the pilot light turn it off and do nothing else for at least five minutes to allow any built up gas to dissipate. After the five minutes have expired, turn the gas valve to the PILOT position. If there is a safety or reset button, push and keep the button depressed. Hold a lighted match to the hole where the pilot light should be and turn the gas valve to the on position. When the pilot light is burning, release the reset/safety button. If your furnace does not have a reset/safety button or gas valve, just hold a lighted match up to the pilot light hole. If the pilot flame wont stay lit after several attempts you should contact a professional.
If you can't get the pilot light to stay lit and the appliance has a thermocouple, the problem may be that it's faulty. The thermocouple has a heat sensor attached to a solenoid. When not heated by the pilot light the solenoid closes the gas supply line to keep dangerous gas from filling your home. If any part of the thermocouple is broken, the pilot light wont stay lighted and must be replaced.
Start replacing the thermocouple by unscrewing the copper lead and the connection nut inside the threaded connection to the gas line. Under the mounting bracket at the thermocouple tube, unscrew the bracket nut that holds the tube in place. Insert the new thermocouple into the hole in the bracket with the steal tube facing up and the copper lead facing down. On the underside of the bracket, screw the bracket nut over the tube and then push the connection nut into the threaded connection where the copper lead connects to the gas line. Screw the nut firmly into place, but do not over tighten. Both the bracket nut and the connection nut should only be slightly tighter than what you can do with your hands.
Still no luck keeping the pilot lit? Well, unfortunately, its time to call a pro since the problem may be with the gas line itself. Problems like this are best left in the hands of an expert.
For other related information about how to maintain a pilot light