What to Do if a Gas Furnace Pilot Light Won't Stay Lit

A blue flame against a black background.
What You'll Need
Fine-grained sandpaper
Clean cloth

A properly functioning pilot light in your furnace means reliable heat in your home and safety from the possibility of gas leaks. Naturally, an unreliable pilot light is something that you should worry about and fix as soon as you notice it. However, there are many different things that can cause a pilot light to repeatedly go out. What follows should give you a good idea of how to deal with the most common problems.

Open the Furnace

To begin, you will need to access the pilot tube and the thermocouple in order to observe them and figure out what problems are present. Begin by turning your pilot light off, if it is not already. Next, turn off the flow of gas to your furnace completely using the shutoff valve. It should be nearby or even on your furnace. Once you have done this, allow your furnace to cool down for at least 30 minutes so it is safe to open, then open the hatch covering your pilot light and look inside.

Check the Thermocouple

Your furnace's thermocouple, if it works normally, checks to see whether the pilot light is on or off. Thermocouples detect pilot lights by sensing the heat they produce. If it determines that the pilot light is off, it shuts down the flow of gas. While this is an excellent safety feature, a faulty thermocouple may decide arbitrarily that your pilot light is off when you want it on, shutting down your pilot light and your furnace.

The first common problem a thermocouple can have is being bent out of shape. This causes it to be out of place and unable to detect any heat, so it automatically shuts down the instant you are not telling the pilot light to be on. If you suspect this is the case, or you have noticed that your pilot light simply will not stay on for more than a few seconds, turn the pilot light on and see if it is actually aimed at the thermocouple. If it is not, you can bend the thermocouple back into alignment with the pilot tube—but only after allowing everything to cool.

If this is not the problem you are having, the thermocouple may just be dirty. You can clean it off with fine-grained sandpaper.

Check the Pilot Tube

It is possible for the pilot tube in your furnace to become blocked, making the pilot light go out. Additionally, a dirty pilot tube will be less reliable than a clean one. While this is a less common problem, it still may be the cause of your pilot light's problems. There is no good way to check if your pilot tube is dirty, but fortunately the process for cleaning it is short. When the furnace is cool and the gas off, simply get out a needle and put it inside the pilot tube, scraping the sides clean. Once you have done this, you can test out your pilot light again to see if it is working any better.