Causes of Furnace Ignitor Failure and How to Prevent It

The furnace ignitor is a small part with a big role: it lights the burner to heat a home. When an ignitor fails, heating stops and repairs can be urgent and costly. This article explains the common causes of furnace ignitor failure, how to diagnose problems, preventive maintenance tips, and replacement considerations to help homeowners keep HVAC systems reliable.

Common Cause	Typical Signs	Prevention
Age and Wear	Intermittent ignition, visible cracks	Scheduled inspection and timely replacement
Electrical Issues	No voltage, erratic operation	Check wiring, tighten connections, protect from surges
Dirty Burners/Flame Rollout	Delayed ignition, sooting	Annual cleaning and combustion tune-ups
Overheating/Cycling	Shorted life span	Correct airflow, proper thermostat settings
Moisture/Corrosion	Visible oxidation, early failure	Moisture control, replace corroded components

How Furnace Ignitors Work

Furnace ignitors come in two main types: hot surface ignitors (HSI) and spark or pilot ignitors. HSIs use a silicon carbide or silicon nitride element that glows hot to ignite gas, while spark ignitors create a high-voltage arc to light a pilot or main burner.

Both types rely on proper electrical voltage, intact wiring, and appropriate combustion conditions to function. Understanding the technology helps isolate failures to electrical, mechanical, or environmental causes.

Primary Causes Of Ignitor Failure

1. Natural Wear And Age

Ignitors have a finite lifespan. Hot surface ignitors typically last 3–5 years depending on usage and operating conditions. Repeated thermal cycling causes micro-cracks and material fatigue that eventually lead to breakage or failure to reach ignition temperature.

2. Electrical Problems

Voltage supply issues, loose or corroded wiring, faulty control boards, and bad relays are common causes. Low voltage can prevent an HSI from reaching ignition temperature while surges can crack brittle elements.

Key electrical signs include no voltage at the ignitor terminals, blown fuses, or error codes on the furnace control board.

3. Overheating And Excessive Cycling

Short cycling sparked by incorrect thermostat settings, blocked airflow, or oversized equipment increases the number of on/off cycles and shortens ignitor life. Continuous thermal stress accelerates deterioration of HSI elements.

4. Dirty Burners And Combustion Issues

Deposits on burners, cracked heat exchangers, or poor gas pressure can change the ignition environment. Persistent delayed ignition causes repeated high-stress conditions on the ignitor and can lead to soot or flame rollout that damages components.

5. Moisture, Contaminants, And Corrosion

Condensation, humidity, or chemical contamination can corrode terminals and weaken the ignitor material. Outdoor vents or poorly sealed furnace cabinets allow moisture to reach sensitive parts, reducing life expectancy.

6. Mechanical Damage And Mishandling

Hot surface ignitors are brittle and can crack from impact during maintenance or installation. Even slight contact with fingers, tools, or debris can cause invisible microfractures that later cause failure.

7. Manufacturing Defects Or Poor Installation

Occasional defective units or improper installation (incorrect mounting, wrong part for the model) lead to premature malfunction. Using aftermarket parts not matched to the furnace specifications increases risk.

Symptoms Of A Failing Ignitor

Homeowners and technicians should watch for these common symptoms: furnace fails to start, long ignition delay, intermittent heating, furnace attempts to ignite repeatedly then locks out, visible cracks in HSI, and error codes indicating ignition failure.

Documented patterns—like failure after a recent service—point to installation or accidental damage.

How To Diagnose Ignitor Problems Safely

Diagnosing ignitor failure should follow safety protocols: shut off power and gas before inspection. Visual inspection can reveal cracks or discoloration in HSIs and loose connections.

Electrical testing with a multimeter measures resistance for HSIs—typical values often range from 40 to 90 ohms but vary by model. A lack of continuity or open circuit indicates a failed ignitor. For spark ignitors, voltage checks and observation of spark during operation are used.

Always consult the furnace manual for model-specific resistance values and diagnostic sequences.

Step-By-Step Diagnostic Checklist

1. Check furnace error codes and the control board LED blink pattern.
2. Verify thermostat calls for heat and check power to the furnace.
3. Inspect the ignitor visually for cracks, chips, or discoloration.
4. Test ignitor resistance with a multimeter; compare with manufacturer specs.
5. Confirm voltage is being supplied to the ignitor during the ignition cycle.
6. Inspect burners, flame sensor, and gas valve operation for related issues.
7. Look for moisture, corrosion, or wiring damage in the cabinet.

Replacement And Repair Considerations

When an ignitor fails, replacement is often the only reliable fix. HSIs are consumable items; replacing with OEM or high-quality aftermarket parts ensures better fit and lifespan. Technicians should handle elements carefully and avoid touching hot surfaces with bare hands.

Replacement cost varies: parts range from about $40 to $150 for HSIs, with labor adding $75–$250 depending on service call rates. Spark ignitor systems can cost more due to additional components.

Preventive Maintenance To Extend Ignitor Life

Regular maintenance reduces ignitor failure risk. Routine tasks include cleaning burners, replacing air filters every 1–3 months, checking flame sensors, inspecting wiring, and scheduling annual professional tune-ups to adjust gas pressure and combustion.

Key preventive steps: maintain proper airflow, minimize short cycling, protect electronics from surges, and control moisture in mechanical rooms.

Practical Tips For Homeowners

• Replace dirty air filters promptly to prevent restricted airflow and overheating.
• Keep the area around the furnace clean and dry to limit contaminants and moisture.
• Record furnace performance and error codes to help technicians diagnose recurring issues.
• Consider a surge protector or dedicated circuit for HVAC electronics in areas prone to electrical storms.
• When replacing parts, use model-specific ignitors and keep the furnace manual for reference.

When To Call A Professional

Homeowners should call an HVAC technician when the furnace shows repeated ignition failures, when electrical testing is required, or when gas control components are involved. Professionals can safely test gas pressure, inspect control boards, and ensure correct replacement and calibration.

Attempting complex electrical or gas repairs without training can be dangerous and may void warranties.

Cost And Warranty Insights

Replacement costs depend on part quality and labor. OEM parts typically cost more but match factory specs. Warranties vary: some ignitors have limited warranties of months to a year; manufacturer-covered systems may include longer protection when installed by authorized contractors.

Keep receipts and service records to support warranty claims and track component longevity.

Common Myths And Misconceptions

One myth is that ignitors never fail if a furnace is well-maintained. While maintenance helps, ignitors are consumable and will eventually need replacement. Another misconception is that any crack is cosmetic; even hairline fractures can cause functional failure under heat.

Timely inspection and replacement are more cost-effective than waiting for complete failure mid-winter.

Frequently Asked Questions

How Long Does A Furnace Ignitor Last?

On average, hot surface ignitors last 3–5 years, though some may fail sooner due to cycling or environmental factors.

Can An Ignitor Be Repaired?

Ignitors are typically replaced rather than repaired because the elements are fragile and repairs are unreliable.

Is It Safe To Start The Furnace With A Cracked Ignitor?

No. A cracked ignitor may break completely or fail to ignite properly, potentially causing repeated lockouts and stress on other components.

Does A Dirty Furnace Cause Ignitor Failure?

Indirectly. Dirt and soot can cause delayed ignition and overheating conditions that shorten ignitor life, so keeping burners and filters clean reduces risk.

Final Notes For Reliable Heating

Furnace ignitors are critical and sensitive components susceptible to wear, electrical faults, and environmental damage. Regular maintenance, careful handling, and timely professional intervention extend service life and maintain safe, efficient heating.

Proactive care and prompt replacement of failing ignitors minimize downtime, prevent collateral damage to other furnace parts, and improve home comfort.