How Spark Ignition Works on a Gas Furnace

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Estimated reading time: 2 minutes


Here’s how a basic gas furnace works:

  1. The thermostat sends a signal to the furnace to turn on when the temperature in the home falls below the set point.
  2. The ignition control receives this signal and opens the gas valve to allow gas to flow into the furnace.
  3. The ignition control then sends a signal to the spark ignition device, which creates a spark to ignite the gas.
  4. The gas is ignited and begins to burn, heating the air in the furnace.
  5. The heated air is circulated through the ducts and into your rooms, raising the temperature to the set point.
  6. When the temperature in the home reaches the set point, the thermostat sends a signal to the furnace to turn off, and the gas valve is closed, stopping the gas flow to the furnace.

Overall, the gas ignition system in a residential furnace is an important part of the heating system that helps ensure the furnace’s safe and efficient operation.

Let’s Get Technical

Technically speaking, here’s an in-depth review of how a faulty spark ignition device (and other issues) is evaluated on a gas furnace.

The video is an excellent example of the numerous components that must work together on a modern furnace. Still, it is an even better example of why you want an experienced technician working a service call. Because gas is so volatile, the furnace control board must handle many checks and balances. One problem can have multiple solutions.

As mentioned in the video, an outdoor package unit is (because they’re located in a humid environment) prone to corrosion and moisture. Maintaining rusty components could be the most significant challenge, and you should understand this system’s risk (or upkeep).

I follow A/C Service Tech for inspection tips and info. They produced this video.


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