How Do Pilot Lights Work?

Furnaces have evolved quite a bit over the last few decades. Those of you who have lived in rural areas far from gas lines, have nice cabins, or have lived a few decades longer than me might have even used wood-burning furnace in order to heat their homes. Those have largely fallen out of favour; gas and electric furnaces are in, which means we don’t all need a small forest in our backyards. Even gas furnaces have evolved considerably, however, but those with a furnace built in the 80s will probably have an interesting little feature in their furnace; the pilot light.

Pilot lights serve a fairly straightforward purpose in gas furnaces; they ignite the gas that’s flowing through the furnace in order to create heat. When the furnace is turned on, gas flows from a valve into the burner, where it is lit. A small amount of gas is also fed from a valve into the pilot light, which is how it keeps burning all the time.

There does seem to be a bit of a safety problem with the pilot light in this case; if gas is flowing continually to the pilot light, when it blows out, where does that gas go? Were it to just flow freely, it could accumulate throughout your house, hazardous to breathe and even more dangerous if it ignites. Fortunately, furnace manufacturers came up with a pretty innovative solution to the problem; the gas valve is closed when the pilot light is off. You might think it uses an electrical current to do this; that’s astute, but it doesn’t quite paint the whole picture. If your home were to experience a power outage, the valve would still need to be able to shut off; how does it generate the electricity needed to close?

The answer is a fascinating little phenomenon known as the thermoelectric effect. Without delving deep into the physics of it, what you need to know is that when a metal is heated on one side but cooler on the other, an electrical current will flow through it. Using this effect, the pilot light heats a metal in order to create an electrical current that holds the valve open. When the pilot light shuts off, the metal cools, the electrical current stops flowing, and the valve closes. That means every time a pilot light shuts off, the valve will shut too; that’s when you have to press a button on your furnace to open the valve, light the gas to create another pilot light, and wait for the metal to heat up again so the valve can remain open.

Anyone who has had to relight a pilot light knows they can be a bit of a pain! Sure, it’s not as bad as burning wood, but there’s a lot of wasted gas that goes to keeping those things lit, so you should probably upgrade to a better, more fuel-efficient furnace. Get a professional furnace maintenance company to look at your setup and propose heating solutions that will fit your budget!

I would like to send my appreciation to Robert at Provincial Heating & Cooling for offering at true 24 hour service. Our water heater decided to leak Christmas morning and with Family and guests visiting, no hot water was no option. I called your company’s phone number and reached Michael, one of your techs, he was professional in every area, and we had hot water in less then two hours. I will recommend your company to all my friends and neighbors. Great service and Merry belated Christmas. Thank you.

Gerry L
324 A Keewatin St Winnipeg, Manitoba