How pilot lights work

Recently I re-lit my floor furnace. While I was at it, I took lots of pictures and posted them on Facebook, along with lots of little comments. One of the comments I made was that the pilot light of the floor furnace generates enough electricity to operate the thermostat. (In the event of an ice storm bad enough to cause a power outage, this is a handy little feature.) A viewer of this Facebook album asked, reasonably enough, does the pilot light really generate electricity?

Well, yes it does, it says so right in the manual for the floor furnace. But my manual doesn't say how this works. Fortunately the web site How Stuff Works seems to have the answer to this question.

Thermocouples generate electricity directly from heat. They take advantage of an electrical effect that occurs at junctions between different metals. For example, take two iron wires and one copper wire. Twist one end of the copper wire and one end of one of the iron wires together. Do the same with the other end of the copper wire and the other iron wire. If you heat one of the twisted junctions with a flame and attach the two free iron wires to a volt meter, you will be able to measure a voltage.

In a pilot light, one of the junctions of a thermocouple is sitting in the pilot light's flame. The electricity that is created runs to a small electromagnetic valve and holds it open. If the pilot light blows out, the thermocouple quickly cools off. It stops generating electricity and the valve closes.

Pretty neat, huh?