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The burner in your gas furnace is ignited either by an electronic ignition, found in most modern furnaces, or with a standing pilot program fire, which is common in older-style furnaces that have an annual fuel use efficiency ( AFUE ) rat of less than 80 percentage. A accelerator furnace ‘s standing navigate, in which the flame is lit at all times, is sometimes referred to as a fly light .

No matter what you call it, its purpose is to serve as a small ignition flare for the accelerator burner. When the thermostat signals for boast to be delivered from the flatulence valve to the burner, the standing pilot ignites the boast flowing to the burners to heat the air in the combustion chamber. When this fiddling flame fails to operate properly or goes out, it ‘s one of the most common reasons that a accelerator furnace fails to operate .

Because this digest navigate fire ( and its acquaintance, the thermocouple ) makes or breaks your furnace ‘s operation, it ‘s worth spending some time to learn how it works. Understanding the furnace navigate is a crucial function of troubleshooting your gas furnace .

How the Thermocouple and Standing Pilot Work

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The thermocouple is an electronic device that senses if the pilot program flame is hot enough to ignite natural gas or propane fuel flowing to the burner. If the thermocouple thinks it ‘s safe, then it allows the main flatulence valve in the pilot burner assembly to open up and stay open. If the thermocouple or flare detector does not sense enough inflame from the pilot burner flame—such as when the original is extinguished—then the thermocouple shuts off the gas valve delivering gas to the burners .

The thermocouple—which is technically called a thermocouple junction—is a device that contains two metallic wires welded at the ends and placed inside a protective alloy case. The thermocouple detector is found at the clientele end of the navigate fire and is designed to be placed in the hottest contribution of the flare. The early end is connected to the pilot valve body .

As the thermocouple heats up, it produces a modest amount of electricity. When heating system is called for and it gets hot enough from the heat of the navigate flare, it sends a signal to open the gas valve by using a solenoid operated by a 24-volt transformer. The thermocouple calls the shots, and by converting estrus to an electrical bespeak, it allows the gas valve to open .

once the valve is loose, gas is constantly supplied to the pilot and to the boast burners, as called for by the thermostat. If the pilot goes out, then the thermocouple gets cold and does n’t produce an electric signal to open the boast valve ‘s solenoid, so the natural gas valve shuts off the gas supply to the pilot and burners .