Gas Furnace

7 Facts on Gas Furnace Ignitor Sensor

Gas Furnace Ignitor Sensor

Gas Furnace Ignitor Sensor: Operational Mechanism, Types, and Troubleshooting

A gas furnace ignitor is a critical component that ensures the safe and efficient ignition of the fuel in a gas furnace. It plays a crucial role in the furnace’s operation, detecting the presence of a flame and initiating the ignition process. Understanding the operational mechanism, types, and troubleshooting of a gas furnace ignitor is essential for maintaining the proper functioning of your heating system.

What is the Operational Mechanism of a Gas Furnace Ignitor?

The gas furnace ignitor operates in a two-step process:

  1. Detection of Flame Presence: The ignitor, often accompanied by a flame sensor, detects whether a flame is present in the burner assembly. If a flame is detected, the ignitor continues to allow gas flow; otherwise, it shuts off the gas valve to prevent unburned gas from leaking into the system.

  2. Ignition Process: When the thermostat calls for heat, the furnace control board initiates the ignition sequence. This involves opening the gas valve and activating the ignitor. The ignitor generates heat or a spark to ignite the gas flowing through the burners.

What are the Types of Gas Furnace Ignitors?

There are two main types of gas furnace ignitors:

  1. Hot Surface Ignitors:
  2. These ignitors use a resistive heating element (usually a silicon carbide or silicon nitride rod) that heats up when an electrical current is applied. Once hot enough, the element ignites the gas flowing through the burners.

  3. Electrical Specifications: Typically operates at 120V AC and draws a few amps (usually around 1-2 amps) during the heating phase.

  4. Spark Ignitors:

  5. These ignitors produce a high-voltage spark to ignite the gas. They are often used in newer furnaces and are known for their reliability and efficiency.
  6. Electrical Specifications: The spark is generated by a high-voltage transformer, typically in the range of 5,000 to 10,000 volts, but the control circuit usually operates at 24V AC.

What are the Signs of a Faulty Gas Furnace Ignitor?

  1. Delayed Ignition: If the furnace takes longer than usual to ignite, it could indicate a problem with the ignitor or the associated circuitry.

  2. Flickering Flame: A flame that flickers or is unstable may suggest that the ignitor is not providing a consistent spark or heat.

  3. Furnace Not Igniting at All: If the furnace fails to ignite, it could be due to a faulty ignitor, a malfunctioning flame sensor, or issues with the gas supply or electrical connections.

How to Troubleshoot a Gas Furnace That Won’t Ignite?

To troubleshoot a gas furnace that won’t ignite, follow these steps:

  1. Check Power and Gas Supply: Verify that the power and gas supply to the furnace are turned on and functioning correctly.

  2. Inspect the Ignitor: Remove the access cover to the burner assembly and inspect the ignitor for visible damage or wear. For hot surface ignitors, check for cracks or breaks in the heating element.

  3. Clean the Flame Sensor: Remove the flame sensor and clean it with an emery cloth to remove soot and debris. This can often resolve issues where the furnace is not igniting due to a dirty sensor.

  4. Test the Ignitor Circuit: Use a multimeter to check the voltage and resistance in the ignitor circuit. For hot surface ignitors, measure the resistance across the heating element; it should be within the manufacturer’s specified range. For spark ignitors, check the high-voltage output of the transformer.

  5. Check Electrical Connections: Ensure all electrical connections to the ignitor and flame sensor are secure and not corroded.

  6. Replace the Ignitor if Necessary: If the ignitor is found to be faulty, replace it with a new one. Ensure the replacement is compatible with your furnace model.

What are the Costs and Time Required for Ignitor Replacement?

  • Costs:
  • The cost of replacing a gas furnace ignitor can range from $50 to $200, depending on the type and brand of the ignitor.

  • Labor costs, if hiring a professional, can add an additional $100 to $300.

  • Time Required:

  • Troubleshooting can take anywhere from 30 minutes to several hours, depending on the complexity of the issue.
  • Replacing the ignitor typically takes about 1-2 hours, including disassembly and reassembly of the furnace components.

Reference:

  1. Snell Heating and Air: 6 Signs the Flame Sensor in Your Furnace Has Gone Bad
  2. Quality Heating, Cooling & Plumbing: 7 Signs of a Bad Flame Sensor in a Furnace
  3. HVAC.com: A Complete Guide to Furnace Flame Sensors

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