Why Furnace Ignitors Keep Failing and How to Fix It

The phrase “Furnace Ignitor Keeps Going Bad” reflects a common problem homeowners face when gas furnaces fail to light reliably. This article explains why ignitors fail, how to diagnose repeating ignitor problems, effective repairs, preventive maintenance, and cost expectations. The guidance is practical, safety-conscious, and tailored to typical U.S. residential systems.

Symptom	Likely Causes	Typical Fix
No Spark Or Glow	Failed Ignitor, Loose Wiring	Replace Ignitor, Tighten Connections
Intermittent Lighting	High Heat, Faulty Control Board	Check Heat Cycling, Replace Board If Needed
Frequent Failures	Voltage Issues, Vibration, Moisture	Inspect Transformer, Mounting, Seal Ducts

How Furnace Ignitors Work

Furnace ignitors are the component that initiates combustion in a gas furnace. Most modern furnaces use silicon nitride hot surface ignitors (HSIs) that glow orange when heated by electric current, while older systems may use spark ignitors. The ignitor draws a specific voltage and current; when it reaches operating temperature it permits the gas valve to open and burners to light.

Common Reasons An Ignitor Keeps Going Bad

Understanding repeated ignitor failure requires looking beyond the part itself to system conditions that stress it. Common causes include overheating from poor airflow, electrical faults, vibration and mechanical stress, moisture and corrosion, and improper replacement parts or installation.

Poor Airflow And Overheating

Restricted return vents, dirty air filters, closed registers, or a failing blower can cause the furnace cabinet to overheat. Heat cycling shortens ignitor life because HSIs are brittle ceramics that degrade with repeated thermal shock.

Electrical Problems

Voltage spikes, an underpowered transformer, loose wiring, or failing relays and control boards can subject the ignitor to incorrect voltages. Both over-voltage and repeated on/off cycling damage the ignitor.

Vibration And Mechanical Stress

Loose mounting hardware, unbalanced blowers, or ductwork vibration can fracture the thin ceramic of HSIs. Even slight flexing during start-up can create microscopic cracks that rapidly propagate.

Moisture, Corrosion, And Contaminants

Condensation in the furnace area or corrosive atmospheres (near pools, coastal homes) can corrode connections and damage the ignitor surface. Dust, soot, or oil can also cause hotspots and premature failure.

Incorrect Parts Or Poor Installation

Using the wrong model ignitor or improper torque when installing can cause misalignment, poor thermal contact, or connection issues that shorten component life.

Diagnosing Repeated Ignitor Failures

Systematic diagnosis isolates whether the ignitor is the root cause or a symptom of another system fault. A methodical approach reduces wasted parts and repair costs.

Visual Inspection

Look for hairline cracks on HSIs, burn marks on terminals, melted insulation, or signs of corrosion. Check mounting brackets, orientation, and whether the ignitor or bracket touches any moving parts.

Electrical Testing

Use a multimeter to measure resistance and continuity according to manufacturer specs. Typical HSI resistance ranges differ by model; a very high or open reading indicates failure. Also test transformer voltage and inspect control board output during the ignition sequence.

Check Airflow And Heat Patterns

Measure static pressure and inspect filters, vents, and blowers. Verify proper flue draft and ensure the furnace is not overheating. An overtemp condition often correlates with frequent ignitor replacement.

Analyze Failure Timing

Record when failures occur: only during extreme weather, after maintenance, or randomly. Patterned failures often point to environmental or operational causes rather than isolated component defects.

Practical Repairs And Solutions

Repair selection depends on diagnosis. Replacing the ignitor alone may be sufficient for a single isolated failure, but repeated failures require addressing underlying causes.

Replace The Ignitor Correctly

When replacing an ignitor, match the OEM part number or an equivalent rated for the furnace’s voltage and wattage. Handle HSIs carefully; oils from skin reduce lifespan. Tighten terminals and mounting screws to manufacturer torque recommendations without over-tightening.

Fix Airflow Problems

Replace or clean dirty filters, unblock returns and supply registers, inspect and clean the blower wheel, and confirm the blower motor runs at correct speed. Improving airflow reduces cabinet temperature and thermal stress on the ignitor.

Address Electrical Issues

Have a licensed technician check transformer output, control board function, and relay behavior. Replace failing transformers, tighten wiring connections, and update corroded terminals. Surge protection for the HVAC circuit can help in areas with frequent voltage spikes.

Reduce Vibration And Mechanical Stress

Secure mounting hardware, replace worn blower bearings, and use vibration-dampening mounts where appropriate. Reposition ignitor or bracket if it contacts other components during operation.

Control Moisture And Corrosion

Seal the furnace cabinet from damp basements, install insulation in unconditioned spaces, and ensure proper condensation drainage on high-efficiency systems. Replace corroded connectors and apply appropriate dielectric grease on terminals to protect against corrosion.

When To Replace The Entire Ignition System

If failures persist after addressing airflow, electrical, vibration, and moisture issues, the control module or gas valve may be cycling improperly and stressing ignitors. In such cases, replacing the control board or moving from a hot surface ignitor to a spark ignitor is an option but requires professional evaluation due to code and safety considerations.

Cost Considerations And Typical Lifespan

An HSI replacement part typically costs $40–$150 depending on furnace make and model. Labor for a professional replacement averages $100–$300, varying by region and complexity. A correctly installed HSI in normal conditions can last 3–10 years, with average lifespans around 5 years.

Preventive Maintenance To Extend Ignitor Life

Regular maintenance reduces stress on ignitors and extends service life. An annual HVAC tune-up is recommended ahead of heating season to inspect, test, and correct minor issues before they cause repeated ignitor failures.

• Change Filters Every 1–3 Months: Keeps airflow optimal and cabinet temperatures lower.
• Annual Professional Inspection: Technician tests electrical components, checks gas pressure, and inspects ignition sequence.
• Keep Area Dry And Clean: Avoid placing humidifiers or fuel-storage near the furnace; control moisture and dust.
• Address Loud Noises Promptly: Symptoms like rattles or unusual vibrations herald mechanical wear that can harm ignitors.

Safety Tips When Working On Ignitors

Gas and electric components pose serious hazards. Always shut power and gas to the furnace before inspecting or replacing an ignitor. If unsure about testing live circuits, contact a licensed HVAC technician. Carbon monoxide risks increase with improper ignition; ensure flue and venting are clear after repairs.

Frequently Asked Questions

Can Homeowners Replace An Ignitor Themselves?

Capable DIYers can replace an ignitor if the steps are followed carefully and utilities are shut off. However, diagnosing repeated failures and addressing electrical or gas issues is best handled by a licensed technician.

How Often Should An Ignitor Be Replaced?

There is no fixed schedule; replacement is condition-driven. With good maintenance, ignitors often last several years. Repeated failures indicate other system problems rather than routine replacement needs.

Does Replacing The Ignitor Fix A Furnace That Won’t Start?

Not always. If the ignitor is confirmed defective it will stop immediate failures, but if the furnace control board, gas valve, thermostat, or airflow issues are present, the problem may persist.

Signs That Point Away From Ignitor Problems

Some furnace no-start conditions are unrelated to the ignitor. These include a dead thermostat, blocked condensate line (on high-efficiency units), defective gas valve, or faulted safety switches. Proper diagnosis differentiates these causes.

When To Call A Professional

Call a licensed HVAC technician if there are repeated ignitor failures despite correct replacement, signs of electrical faults, gas odors, loud mechanical noises, or if any step of diagnosis involves live circuit testing. Professionals ensure safe, code-compliant repairs and can test system-wide issues like improper gas pressure or control board failures.

Key Takeaway: An ignitor that keeps going bad usually signals broader system problems—airflow, electrical supply, vibration, moisture, or improper installation—rather than a single defective part. Thorough diagnosis, correct part selection, and preventive maintenance together stop repeated failures and extend furnace lifespan.