Furnace Spark Ignitor Troubleshooting Guide

The following guide helps diagnose and resolve common furnace spark ignitor problems, offering safe testing steps, cleaning tips, and replacement advice for homeowners and technicians.

Issue	Possible Cause	Quick Action
Ignitor Not Sparking	Broken ignitor, failed transformer, wiring fault	Visual inspection, multimeter test
Intermittent Spark	Loose connection, dirty ignitor, control board issue	Tighten connections, clean, retest
Burner Won’t Light	No spark or weak spark, gas valve issue	Confirm spark, check gas valve, call pro if needed

How A Furnace Spark Ignitor Works

A furnace spark ignitor creates an electrical spark to ignite the gas in the burner assembly. It typically consists of two electrodes separated by a gap and connected to a high-voltage transformer or ignition module.

Key Function: Produce a high-voltage spark at the burner to initiate combustion quickly and reliably.

Common Symptoms Of Ignitor Problems

Recognizing symptoms early prevents further damage. Symptoms include no spark, weak or inconsistent sparking, a clicking sound without ignition, burners that fail to light, and the furnace engaging in repeated restart cycles.

Important Note: Similar symptoms can come from a faulty gas valve, control board, or flame sensor, so diagnosis must be stepwise.

Tools And Materials Needed

• Multimeter (AC/DC and continuity)
• Insulated screwdriver set
• Nut drivers or socket set
• Needle-nose pliers
• Soft brush and compressed air
• Replacement ignitor (model-specific)
• Gloves and safety glasses

Safety Precautions Before Troubleshooting

Always cut power to the furnace at the service switch and circuit breaker before accessing internal components. Turn off the gas supply when working near the gas valve or burners.

Safety Reminder: High-voltage components can shock even when the furnace is off; wait for capacitors to discharge and use insulated tools.

Initial Visual Inspection

Start with a visual inspection of the ignitor and surrounding components. Look for cracks, chips, any white or gray powder on ceramic ignitors, burns on wiring, or loose terminals. A visibly damaged ignitor typically requires replacement.

Check Wiring: Ensure wires are connected firmly and there are no melted insulation or corrosion signs.

Step-By-Step Troubleshooting

1. Confirm The Symptom

Run the furnace through a call for heat and observe the ignitor during the start sequence. Determine whether there is no spark, sporadic sparking, or a weak spark.

2. Listen And Observe

A rapid clicking without flame often indicates a spark or gas ignition failure. If clicking is absent, the ignition module or transformer may not be energizing.

3. Check Error Codes And LED Indicators

Modern furnaces display diagnostic codes via an LED on the control board. Record any blinking patterns and consult the furnace manual to interpret the code; codes can point directly to ignition, flame sensing, or control board faults.

4. Test For Spark Visually

With the gas off and power on for the ignition sequence, observe the burner area for a visible spark. Use a mirror or flashlight to see into tight spaces. No visible spark suggests an ignitor or ignition transformer problem.

How To Test A Spark Ignitor With A Multimeter

Testing verifies whether the ignitor has continuity and is within manufacturer resistance ranges. Refer to the furnace manual for the correct ohm value.

Resistance Test

Disconnect power, remove the ignitor connector, and set the multimeter to the ohms scale. Place probes on the ignitor electrodes or connector pins. A reading of infinite resistance indicates an open circuit and a failed ignitor.

Typical Range: Many hot surface ignitors read 40–160 ohms; spark ignitors differ, so check the spec sheet.

Voltage Test For Ignition Transformer

With caution and power restored, measure secondary voltage at the ignition transformer or module during a call for heat. High voltage is expected; no output points to transformer/module failure. Only qualified individuals should perform live high-voltage checks.

Cleaning And Minor Repairs

If the ignitor is intact but dirty or covered in deposits, cleaning may restore normal operation. Use a soft brush or compressed air; avoid abrasive contact or touching the ignitor element directly with fingers.

Wiring Connections: Tighten loose terminals and replace any frayed wires using appropriate connectors and heat-resistant wiring where required.

Replacing The Spark Ignitor

If tests show a failed ignitor or it is cracked, replacement is usually straightforward. Match the replacement part number to the furnace model to ensure compatibility.

1. Turn Off Power And Gas: Safety first.
2. Access The Burner Compartment: Remove the furnace panel.
3. Disconnect The Ignitor: Note the wiring orientation or take a photo.
4. Remove Mounting Hardware: Carefully slide out the ignitor assembly.
5. Install The New Ignitor: Avoid touching the element; secure and reconnect.
6. Restore Power And Test: Run the furnace through a start cycle to confirm operation.

Tip: Keep the new ignitor stored in a clean place until installation to avoid contamination.

Possible Causes Beyond The Ignitor

Not all ignition issues originate with the ignitor. Common related causes include a faulty ignition transformer/module, clogged burners, gas valve failure, blocked gas supply, weak control board relays, or issues with the thermostat signal.

Diagnostic Sequence: Confirm ignitor health first, then test the ignition module, gas valve operation, control board outputs, and flame sensing components if problems persist.

When To Call A Professional

Call a licensed HVAC technician if the troubleshooting steps do not resolve the issue, if high-voltage testing is required and the user is not qualified, or if the problem points to gas valve or control board replacement.

Reasons To Hire A Pro: Gas safety, sealed combustion systems, complex control diagnostics, and warranty considerations.

Preventive Maintenance To Extend Ignitor Life

Regular furnace maintenance reduces ignition problems. Suggested actions include annual professional tune-ups, periodic cleaning of burners and combustion chambers, inspecting wiring and connections, and replacing filters to maintain proper airflow.

Maintenance Tip: Maintaining a clean burner environment and stable gas pressure helps ignitors last longer and reduces repeated ignition cycles.

Cost Considerations

Replacement ignitors vary by furnace type and model; a homeowner-grade ignitor typically costs $20–$100. Professional labor and diagnostic fees can raise total expense substantially, often $150–$400 depending on region and service complexity.

Budgeting Advice: Compare OEM parts versus high-quality aftermarket options and verify technician credentials and warranty coverage.

FAQ: Quick Answers To Common Questions

How Long Do Spark Ignitors Last?

Ignitor lifespan varies with usage and environmental factors; many last 3–10 years. Frequent cycling, dirty conditions, and voltage irregularities shorten life.

Is It Safe To Touch An Ignitor?

No. Oils from skin and fragile ceramic parts can damage ignitors. Always handle by mounting bracket and wear gloves when necessary.

Can A Dirty Ignitor Cause Frequent Cycling?

Yes. If the ignitor fails to produce a reliable spark, the control board may attempt multiple restarts, causing repeated cycling and increased wear.

What About Flame Sensors?

A flame sensor detects combustion and can trip the system if fouled. After ignitor repair, clean the flame sensor to ensure stable operation.

Additional Resources And References

Manufacturers’ manuals, HVAC trade associations, and appliance safety sites provide detailed specifications and safety guidance for specific furnace models. Consult these resources when in doubt.

Final Note: Systematic diagnosis saves time and money; begin with safe visual checks and basic electrical tests before replacing parts.