How to Identify and Fix a Bad Ignitor on Your Furnace

A furnace ignitor is a crucial component responsible for lighting the burners and initiating the heating process. When the ignitor malfunctions or fails, the furnace won’t heat your home effectively. Recognizing the signs of a bad ignitor and understanding how to repair or replace it can save time and avoid costly repairs. This article provides detailed insights into diagnosing bad furnace ignitors, troubleshooting tips, and guidance on replacement to keep your heating system running efficiently.

Aspect	Details
Component	Furnace Ignitor (Hot Surface Ignitor or Spark Ignitor)
Primary Function	Ignites burner for heat generation
Common Problems	Cracked ignitor, failure to glow or spark, intermittent ignition
Symptoms of Failure	No heat, clicking sounds, furnace cycles without flame
Replacement Cost Range	$100 – $400 (parts and labor)

What Is a Furnace Ignitor and Why It Fails

The furnace ignitor is an essential component that provides the initial spark or heat to ignite the gas burner. There are two primary types:

• Hot Surface Ignitor (HSI): An electrically heated element glowing red-hot to ignite the gas.
• Spark Ignitor: Creates a spark to ignite the gas burner, common in older or some modern furnaces.

Ignitors are subject to wear and tear over time. Exposure to heat cycles causes material degradation, and environmental dust or debris can damage the surface or wiring. When the ignitor wears out, cracks form, or it stops functioning, the furnace fails to light, leading to cold indoor temperatures.

Common Signs and Symptoms of a Bad Furnace Ignitor

Identifying a faulty ignitor early can prevent system breakdowns. Common symptoms include:

• No heat: The furnace won’t produce warm air despite the thermostat calling for heat.
• Repeated clicking sounds: The furnace attempts to ignite but fails repeatedly.
• Delayed ignition: Ignition takes significantly longer than usual.
• Intermittent heating: The furnace works sporadically due to irregular ignition.
• Visible cracks or damage: Physical inspection reveals cracks or brittleness on the ignitor.

How to Diagnose a Bad Furnace Ignitor Safely

Accurate diagnosis is crucial before considering replacement. Here are steps homeowners or technicians use to test ignitors safely:

Visual Inspection

Turn off the furnace and power supply, then remove the access panel to inspect the ignitor. Look for visible cracks, breaks, or discoloration. Any damage usually means replacement is required.

Test With a Multimeter

Use a digital multimeter set to measure resistance (ohms). Disconnect the ignitor wiring and measure resistance across the terminals.

• A healthy hot surface ignitor typically measures between 40-90 ohms.
• A reading of “infinite” or zero indicates a broken or shorted ignitor.

Observe Furnace Behavior

If the ignitor glows faintly or not at all during startup, this indicates a bad ignitor. Additionally, no spark in spark ignitors during the ignition sequence confirms failure.

Common Causes That Lead to Furnace Ignitor Failure

Understanding why ignitors fail helps in preventing future issues:

• Age and wear: Ignitors naturally weaken over years of heating cycles.
• Electrical issues: Voltage fluctuations or faulty wiring can damage the ignitor.
• Dirt and debris: Dust accumulation causes overheating or physical damage.
• Mechanical shocks: Rough handling or vibrations can crack the ignitor.
• Improper installation: Incorrect mounting or wiring sunglasses the ignitor’s lifespan.

Step-by-Step Guide to Replace a Furnace Ignitor

If a bad ignitor is confirmed, timely replacement is essential:

1. Turn off power and gas supply: Safety first—always disable the furnace before working.
2. Access the ignitor: Remove the furnace panel to locate the ignitor near the burner assembly.
3. Disconnect wiring: Carefully unplug the ignitor wires, noting orientation.
4. Remove the ignitor: Unscrew or unclip the ignitor from its mount. Handle gently, as ignitors are fragile.
5. Install the new ignitor: Mount the new ignitor and reconnect wiring exactly as it was.
6. Restore power and test: Turn on the furnace and observe ignition to ensure proper operation.

Note: If uncertain about any step, it is advisable to contact a licensed HVAC technician.

Costs Involved in Furnace Ignitor Repair or Replacement

Service	Cost Range
Ignitor Part	$40 – $150
Labor (Professional Installation)	$100 – $250
Total Estimated Cost	$140 – $400

Costs vary based on furnace model, ignitor type, and service fees from HVAC companies. Many ignitors are easy to replace yourself, but professional help ensures accuracy and safety.

Preventing Future Furnace Ignitor Problems

Regular maintenance can extend the ignitor’s lifespan:

• Schedule annual furnace inspections to clean and adjust components.
• Replace air filters regularly to reduce dust buildup affecting the ignitor.
• Keep the furnace area clean from dust and debris.
• Monitor furnace startup behavior for early signs of ignitor wear.

When to Call a Professional HVAC Technician

While some ignitor troubleshooting and replacement can be done by experienced homeowners, professional service is recommended for:

• Complex furnace models or hard-to-reach ignitors.
• Persistent ignition failure after replacement.
• Electrical issues or gas line concerns.
• Uncertainty about safely handling gas and electrical components.

A licensed technician ensures the furnace operates safely and efficiently.