Pilot light

A pilot light is a small gas flame, usually natural gas or liquefied petroleum gas, which serves as an ignition source for a more powerful gas burner. Originally, a pilot light was kept permanently alight; however, this is wasteful of gas. Now it is more common to light a burner electrically, but gas pilot lights are still used when a high energy ignition source is necessary, as in when lighting a large burner.

The term "pilot light" is also used occasionally for an electrical indicator light that illuminates to show that electrical power is available, or that an electrical device is operating. Such indicators were originally incandescent lamps or neon lamps, but now are usually LEDs.

Common applications include household water heaters, central heating systems, fireplaces, flamethrowers, and hot air balloons. While most commercial kitchens still rely on pilot lights for burners, ovens, and grills, current residential systems utilize an electrical ignition. This is more commonly known as standby on modern remote control fires.

In natural gas furnaces, water heaters, and room heating systems, a safety cut-off switch is normally included so that the gas supply to the pilot and heating system is shut off by an electrically operated valve if the pilot light goes out. This cut-off switch usually detects the pilot light in one of several ways:

The above methods are examples of the use of "fail-safe" safety protection.

In domestic heating systems with pilot lights it has been estimated that half of the total energy usage is from the pilot light, with each pilot light on average using between 70 and 500 watts of gas power (between 8 and 16 gigajoules/year). The heat from a pilot light in many appliances (furnaces, space heaters, water heaters) is generally released in the same chamber as the primary burner. The energy loss is much smaller for pilot lights in space heaters than other products, because space heaters heat a smaller enclosed space and contribute more significantly to heating the room. The appliance efficiency of a gas fired balanced flue local space heater in pilot light mode is almost equal with the appliance efficiency measured at the reduced power of the appliance, which efficiency is between 65 – 95% based on the low calorific value of the consumed gas, making part of the pilot lights energy consumption into a useful heat.

...
Wikipedia