Having the furnace shut off on a cold winter's night and not starting up again can be a reason to panic. The first thing you'll probably think about is how cold it's going to get in your home and if you are going to be able to stay there until you can get a repairman over to fix the problem. However, furnaces often stop working for reasons that are easy to fix and you should be able to do them yourself without having to call a repairman. If your furnace shuts down and it won't start up again, here is what you should do right away.
The air filter is one of the most important pieces of equipment for your furnace and often one of the most neglected. Yet, a dirty air filter can cause your furnace to shut down and prevent it from starting up again. The problem with a dirty filter is that it stops the air flow into the heat exchanger and this causes the exchanger to overheat. When the heat exchanger overheats, the furnace shuts down as a safety precaution.
So, the first thing you should do is check the air filter in the furnace and see if it's clog. If it is, you need to buy a new one. The size of the filter is written on the side it. Make sure you buy a filter that is the same size as the one you took out of the furnace. By the time you get back and put the new filter in, the furnace will have cooled down and it should start right up.
Check Pilot Light
Sometimes a gust of wind can get onto the furnace area and blow the pilot light out. If the pilot light goes out, the furnace will also shut down as a safety precaution against a dangerous gas leak. You need to restart the pilot.
Find where the draft is coming from and block the opening with anything you can for now (you can do a real fix later). Use towels or cardboard to stuff into the openings to block the draft. Once the draft is blocked, relight the pilot light.
Lighting the Pilot Light
The best thing to use is a long stick match or long butane lighter used to light cooking grills in the backyard. Turn the dial on the pilot light to the "Pilot" position and press down on the button. Light the match and stick into the bottom of the furnace to light the pilot light. You will see a blue flame when the pilot light first starts up. Hold the button down for about a minute while the pilot light heats up. Once the pilot light heats up let the button pop up. If the light stays lit, turn the button to the "On" position. If the pilot light doesn't stay lit, try it again. The furnace should start right up and stay on.
If neither of these things appears to be the problem, you should then call a repairman right away.