Symptoms of a Bad Ignitor on a Furnace: Signs, Diagnosis, and Next Steps

The ignitor is a small but critical component that lights the furnace burners. When it fails, a furnace may behave erratically, produce cold air, or shut down repeatedly. This article outlines the common symptoms of a bad ignitor on a furnace, diagnostic steps, safety tips, replacement guidance, and cost expectations to help homeowners respond effectively.

Symptom	What It Indicates
Repeated Furnace Cycling Without Heat	Ignitor failing to light burners consistently
Clicking Or Clicking Without Ignition	Ignitor attempting to spark but not reaching ignition temperature
No Heat But Blower Runs	Ignitor not lighting; safety controls prevent burner operation
Visible Cracks Or Damage To Ignitor	Physical failure needing replacement
Longer Ignition Delays	Ignitor weakening or inconsistent performance

What Is A Furnace Ignitor And Why It Matters

The furnace ignitor is the component that initiates combustion by generating heat or a spark to light natural gas or propane at the burners. Modern furnaces typically use hot surface ignitors (HSI) made from silicon carbide or silicon nitride and electronic spark ignitors in some systems. If the ignitor fails, the furnace will not produce heat even when other systems appear functional.

Common Symptoms Of A Bad Ignitor On A Furnace

1. Furnace Runs But No Heat

One of the most obvious signs is when the furnace blower runs as expected but no warm air is produced. This usually means the burners are not lighting. If the thermostat calls for heat and the fan operates but the heat exchanger remains cold, a faulty ignitor is a primary suspect.

2. Repeated Cycling Or Short Cycling

If the furnace attempts to light but shuts down shortly afterward and repeats the process several times, it may be repeatedly trying and failing to establish a flame. Short cycling can damage components and reduce efficiency.

3. Clicking Or Clicking Without A Flame

Hearing regular clicking or the normal ignition sequence sounds without flame indicates the control board is commanding ignition but the ignitor is not reaching the temperature or spark required to light the gas. Audible ignition attempts with no flame often point to ignitor deterioration or failure.

4. Longer Ignition Delay

A slowing ignition response — where ignition takes noticeably longer than usual — suggests the ignitor is weakening. Over time HSIs degrade and require more time to reach operating temperature before they can light the gas.

5. Visible Damage Or Cracks On The Ignitor

Physical inspection may reveal chips, cracks, or a broken ignitor element. Because hot surface ignitors are brittle, they can fracture during maintenance or from age. Visible damage is a clear indicator that replacement is necessary.

6. Furnace Runs Then Trips Safety Controls

A failed ignitor can cause repeated lockouts by the furnace control board. If the burners don’t ignite within the control’s set attempts, the furnace often locks out and requires manual reset, a safety feature to prevent gas accumulation.

7. Diagnostic Error Codes Or Lights

Many modern furnaces will display an error code or blink a diagnostic LED when ignition fails. Consult the furnace manual to interpret codes; ignitor failure codes are common and provide a reliable troubleshooting starting point.

How To Diagnose A Bad Ignitor Safely

Safety First

Always turn power and gas off before inspecting a furnace. If uncomfortable with electrical or gas systems, contact a licensed HVAC technician. Improper handling risks electric shock, burns, or gas leaks.

Visual Inspection

With power and gas off, remove the furnace access panel and visually inspect the ignitor. Look for cracks, breaks, or a visibly burnt element. For HSIs, a fractured ceramic element indicates failure.

Using A Multimeter

Measure the ignitor’s resistance with a multimeter set to the ohms scale. Typical resistance values vary by model but are commonly between 40 and 200 ohms for hot surface ignitors. An open circuit (infinite resistance) or dramatically different values indicates failure. Consult the furnace manual for manufacturer-specific specs.

Observation During Ignition Sequence

With a professional or if trained, restore power and observe the ignition cycle from a safe distance. Watch for the ignitor to glow (for HSIs) or spark. If the control board attempts ignition and the ignitor does not glow or spark, the ignitor is likely faulty. Never touch the ignitor while powered.

Common Causes Of Ignitor Failure

• Normal Wear And Thermal Cycling: Repeated heating and cooling cause material fatigue.
• Physical Damage: Mishandling during maintenance or accidental contact with tools.
• Electrical Issues: Short circuits, voltage spikes, or control board faults.
• Contamination: Dirt, oil, or debris can reduce performance and cause overheating.
• Incorrect Voltage Or Wiring: Improper electrical supply can shorten ignitor life.

Immediate Steps To Take If An Ignitor Is Suspected

If the furnace shows signs of ignitor failure, first reset the thermostat to clear any transient faults. If the furnace locks out, follow the manufacturer’s procedure to reset or power cycle. If multiple reset attempts fail, power off the furnace and schedule inspection.

When To Replace The Ignitor Versus Repairing Other Components

If testing confirms the ignitor is defective, replacement is usually the practical solution because ignitors are relatively inexpensive and not repairable. If the ignitor tests good but ignition still fails, investigate the control board, gas valve, wiring, and flame sensor.

How Much Does Ignitor Replacement Cost?

For most residential furnaces, the part cost for a hot surface ignitor ranges from about $25 to $120 depending on the model and OEM vs. aftermarket choice. Labor costs for a qualified HVAC technician usually range from $100 to $300. Total replacement often falls between $150 and $400.

Choosing The Right Replacement Ignitor

Match the replacement ignitor to the furnace model and part number. Using manufacturer OEM parts ensures compatibility and longevity. Aftermarket parts can be economical but verify specifications like resistance, length, mounting style, and connector type.

DIY Replacement: What Homeowners Should Know

Replacement is straightforward for mechanically inclined homeowners but requires careful attention to safety and compatibility. Always turn off power and gas, ground yourself to prevent static damage, and follow manufacturer instructions. Tighten mounting screws to avoid over-torquing fragile elements.

Basic DIY Steps

1. Turn Off Power And Gas To The Furnace.
2. Access The Burner Compartment And Locate The Ignitor.
3. Photograph Wiring And Connector Positions For Reference.
4. Disconnect The Ignitor Wiring Harness And Remove Mounting Screws.
5. Install The New Ignitor, Reconnect Wiring, Restore Power, And Test.

Preventive Maintenance To Extend Ignitor Life

Regular furnace maintenance extends component life. Schedule annual inspections, clean burners and the combustion chamber, replace filters on schedule, and ensure correct airflow. Proper maintenance reduces stress on the ignitor and prevents premature failure.

When To Call An HVAC Professional

Call a licensed HVAC technician if diagnosis requires electrical testing beyond basic multimeter checks, if gas safety issues are suspected, or if the furnace repeatedly locks out after replacing components. Professionals can test control boards, gas valves, and sequence timing safely.

Frequently Asked Questions

Can A Furnace Run With A Bad Ignitor?

The furnace blower may run, but the burners will not light, so the system will not produce heat. Safety controls prevent gas flow if ignition fails repeatedly.

How Long Do Furnace Ignitors Last?

Typical lifespan ranges from 3 to 10 years depending on use, furnace design, and maintenance. Frequent cycling and poor maintenance shorten life.

Is It Safe To Bypass An Ignitor For Testing?

No. Bypassing safety devices or controls can create dangerous gas leaks or fire hazards. Only perform manufacturer-approved diagnostics or hire a professional.

Key Takeaways And Actionable Next Steps

If the furnace shows any of the common symptoms — no heat, repeated cycling, clicking without flame, or visible ignitor damage — homeowners should turn off the system and schedule inspection. For those comfortable with simple diagnostics, a visual check and multimeter resistance test can confirm ignitor failure. Otherwise, contact a licensed HVAC technician for safe diagnosis and replacement.