How Does a Pilot Light Work?

A furnace.

Most homeowners with natural gas furnaces have had the experience of learning that the pilot light on their furnace has gone out. It is necessary to understand how the pilot light functions in order to understand how to relight the pilot light. It is also important to understand how the pilot light interacts with the remainder of the burner system in a safe manner.

Pilot Light Purpose

A pilot light services only one purpose: it supplies the flame—or heat—to ignite natural gas released into the furnace burner when the furnace received an electrical signal from a thermostat that the furnace should begin producing heat.

Pilot Light Function

When the pilot light is working, it is constantly burning a tiny flame that is hot enough to ignite natural gas that comes in contact with this flame.

Safety Factors

If, when the pilot light is extinguished, natural gas were to be released into the burner without being ignited, and if the pilot light were to come on again when this gas is waiting, unignited, in the burner, the gas would explode. To prevent this, a thermocouple is used to tell the furnace to only release gas into the burner when the pilot light is lit.