Furnaces that run off of fuel, such as oil or natural gas, either have a direct ignition system or a standing pilot light. The ignition or pilot light ignites the incoming fuel inside the burner, which then provides the energy for heating the air that is forced through the furnace. If this system fails, then your furnace may blow cold air or it may fail to operate completely. The following can help you determine the cause of the problem.
Fuses and Breakers
One of the simplest reasons for a failed ignition system is a blown fuse. There are fuses in the furnace itself that may require replacement, but it's more likely that the circuit breaker that powers your furnace experienced a power surge and flipped off for safety. Check your circuit breaker box and find the breaker for the furnace. Flip it completely off, then turn it back on. If your direct ignition system begins firing again, then you fixed the problem.
For those furnaces that use a standing pilot light, you can easily check the light to see if it is still burning. Pilot lights can go out for a variety of reasons, most of them harmless. The only time to be concerned is if the light repeatedly goes out or if it burns a color other than blue. Most modern furnace pilot lights can be relit with the push of a button, or you can bring in a repair tech to relight the pilot if you prefer.
Fuel delivery and pilot valves can become dirty over time. Regular maintenance helps prevent this issue. If the valves are clogged with dust, dirt, or other residue, then insufficient fuel will reach either the ignition system or the burner pan. Poor fuel delivery often causes pilot lights to go out repeatedly, to flicker, or to burn a different color such as orange, red, or yellow (instead of blue). A service technician can clean or replace the valves, depending on what is needed.
Gas Line Clog
The air in the fuel lines can prevent the fuel from flowing through, which means the pilot light won't light or the ignition won't fire. Air clogs are more common with filled fuel systems such as oil heaters, but they can still occur with municipal fuel delivery such as in natural gas lines. Your service tech must flush out the lines to clear the clog.
If all else fails, the ignition system may have failed. Direct ignition systems are powered by electricity, which means loose wiring or a blown component could be the cause. A replacement of the ignition system will solve the issue.
Contact a heating repair service for more help with your furnace problems.