Furnace Ignitor Not Working: Causes, Diagnosis, and Fixes

The furnace ignitor not working can leave a home without heat and create safety concerns. This article explains common causes, step-by-step diagnosis, repair options, maintenance tips, and when to call a professional. Readers will learn how to identify a failed ignitor, test components safely, and weigh repair versus replacement choices.

Symptom	Likely Cause	Quick Fix
No spark or glow	Failed ignitor or broken wiring	Replace ignitor
Clicking but no ignition	Gas valve issue or clogged burner	Clean burners; check gas supply
Ignitor glows briefly then fails	Intermittent wiring or failing control board	Inspect connections; test board

How Furnace Ignitors Work

A furnace ignitor lights the burner to start the heating cycle. Modern furnaces commonly use a hot surface ignitor (HSI) made from silicon carbide or silicon nitride, which glows when electrically heated. Some systems use spark ignitors with electrodes that produce a spark to ignite gas. The furnace control module signals the ignitor after safety checks like thermostat call and draft inducer operation.

Common Causes Of A Furnace Ignitor Not Working

Identifying the underlying cause helps prioritize repairs. Common causes include a physically broken ignitor, worn-out element, damaged wiring or connectors, a failing control board, blown fuse or tripped safety switch, insufficient gas supply, or dirty burners preventing ignition.

Physical Damage Or Wear

Hot surface ignitors are brittle and can crack from vibration or improper handling. Cracks or chips render the ignitor unable to reach required temperature. Over time elements degrade and fail to glow even when energized.

Electrical Issues

Broken wires, corroded connectors, or a blown 3-amp or 5-amp fuse in the control board circuit can prevent power from reaching the ignitor. Intermittent connections cause erratic ignition behavior.

Control Board Or Relay Failures

The furnace control board controls timing and provides voltage to the ignitor. Relay failures, faulty output circuitry, or software errors may inhibit ignition despite a good ignitor and gas supply.

Gas Supply And Burner Problems

If the ignitor glows but burners do not ignite, gas valve failure, closed gas shutoff, or clogged burner ports may be the issue. Proper gas pressure and clean burners are necessary for reliable ignition.

Safety Switches And Limit Controls

Pressure switches, flame rollout switches, high-limit switches, and the door/lid safety switch can interrupt ignition if they sense abnormal conditions. These switches sometimes fail or become stuck open, preventing the ignitor from energizing.

Safety First: Precautions Before Testing

Working on furnaces involves electrical and gas hazards. Always shut off power at the furnace switch or breaker and turn off the gas supply before inspecting components. If the homeowner is uncomfortable or unsure, contact a licensed HVAC technician. Carbon monoxide risk increases with improper repairs, so prioritize safety.

Tools And Materials Needed For Diagnosis

Basic tools for diagnosis include a multimeter, non-contact voltage tester, screwdriver set, nut drivers, flashlight, needle-nose pliers, and a soft brush for cleaning. Replacement ignitors and fuses matching furnace specifications may be needed. Use manufacturer parts for best compatibility.

Step-By-Step Diagnostic Checklist

1. Confirm The Symptom

Set the thermostat to call for heat and observe furnace behavior. Note whether the draft inducer motor runs, whether the ignitor glows or sparks, and whether burners light. Record any error codes displayed on the furnace control board or thermostat.

2. Check Power And Fuses

Verify 120V power to the furnace and ensure the furnace switch and breaker are on. Inspect control board fuses. Replace a blown fuse with the correct amperage fuse only after addressing the underlying short or fault causing the blow.

3. Visual Inspection Of Ignitor And Wiring

Open the furnace access panel and inspect the ignitor element for cracks, chips, or breaks. Examine wiring and connectors for burn marks, corrosion, or loose pins. Do not touch a hot surface ignitor with bare hands; oils can damage it.

4. Test For Voltage

With power on and the furnace in the ignition sequence, use a multimeter to check for the expected voltage at the ignitor terminals. No voltage indicates a control or safety switch issue; voltage present with no glow indicates a failed ignitor.

5. Measure Ignitor Resistance

With power off, disconnect the ignitor and measure resistance. Typical HSI resistance ranges from 40 to 90 ohms depending on type; check manufacturer specs. An open circuit or wildly different value suggests replacement.

6. Inspect Safety Switches And Pressure Switch

Verify the inducer motor operates and the pressure switch closes. A clogged vent, blocked condensate drain, or faulty inducer can prevent the pressure switch from signaling the control board, stopping ignition.

Common Repair Actions

Replace A Faulty Ignitor

Replacing a broken or failing ignitor is often the simplest repair. Match the OEM part number or specifications for voltage and shape. Install carefully to avoid cracking. Replace the access panel and test the furnace through multiple cycles.

Repair Or Replace Wiring And Connectors

Repair frayed wires, replace corroded connectors, and ensure tight, clean connections. Use heat-shrink or rated connectors. Poor connections can increase resistance and heat, leading to premature ignitor failure.

Replace Control Board Or Relays

If voltage never reaches the ignitor despite correct inducer and switches, the control board or relays may be at fault. Testing and replacement are more complex; consult the furnace schematic and consider professional service for board replacement and parameter programming.

Clean Burners And Check Gas Valve

When the ignitor glows but burners fail to light, clean burner ports and check that the gas valve receives a call from the control board. Measure gas valve coil resistance per manufacturer specs; if the valve doesn’t open when energized, replace or service the valve.

When To Replace The Entire Furnace

Consider furnace replacement when the system is old (15–20 years), the cost of repairs approaches 50% of a new unit, or efficiency losses and repeated failures make repair uneconomical. New furnaces offer better efficiency, updated safety features, and modern ignition systems that can be more reliable.

Maintenance Tips To Prevent Ignitor Failure

• Schedule annual HVAC tune-ups to clean burners, check controls, and inspect ignitors.
• Replace air filters regularly to maintain airflow and reduce stress on components.
• Keep the furnace area clean and free of debris and dust buildup.
• Ensure vents and flues remain clear to prevent blocked pressure switches and failed inducer cycles.
• Avoid touching hot surface ignitors with bare hands; oil residue degrades elements.

Cost Estimates For Repairs And Replacement

Ignitor replacement typically ranges from $80 to $300 including parts and labor depending on model and accessibility. Control board repairs vary widely, often $300 to $900. Full furnace replacement commonly falls between $3,000 and $8,000 depending on capacity and efficiency. Prices vary regionally and by contractor.

Warranty And Part Sourcing

Check furnace and component warranties before paying for repairs. Many manufacturers offer limited warranties on ignitors and circuit boards. Source replacement parts from authorized dealers or manufacturers to ensure compatibility and maintain warranty coverage.

Troubleshooting Quick Reference

Observed Behavior	Immediate Check	Likely Action
No glow, no voltage	Control board fuse, safety switches	Replace fuse, test switches, replace board if faulty
No glow, voltage present	Ignitor resistance, visual crack	Replace ignitor
Glow but no flame	Gas valve, burner cleanliness	Check gas supply, clean burners, test valve
Intermittent ignition	Wiring, connectors, control board	Repair wiring, inspect board, consider replacement

When To Call A Professional

A licensed HVAC technician should be called for gas valve issues, control board replacement, complex electrical diagnostics, or if the homeowner lacks tools and experience. Professionals can safely handle gas-related repairs, ensure proper combustion, and test for carbon monoxide safety.

Relevant Codes And Safety Standards

Furnace installations and repairs must comply with local building and fuel gas codes and National Fuel Gas Code (NFPA 54) guidelines. Electrical work should conform to the National Electrical Code (NEC). Licensed technicians ensure code compliance and safe operation.

Key Takeaways

Identifying the root cause of a furnace ignitor not working requires systematic checks of power, wiring, safety switches, ignitor condition, and gas supply. Simple replacements are common and affordable, but electrical or gas-system faults call for professional service. Regular maintenance reduces the risk of unexpected failures and extends furnace life.