Gas Furnace Electric Igniter Guide

Electric igniters are the modern standard for starting gas furnaces, replacing standing pilot lights with faster, cleaner, and more reliable ignition. This guide explains how electric igniters work, common failure symptoms, troubleshooting steps, replacement options, costs, and safety tips for homeowners and HVAC technicians.

Igniter Type	Typical Lifespan	Common Failure Signs
Hot Surface Igniter (HSI)	3–5 Years	Cracks, slow heat-up, no glow
Flame Sensor / Intermittent Pilot	2–4 Years	Frequent lockouts, flame loss
Spark Igniter	5–15 Years (control dependent)	No spark, arcing, corroded electrodes

How A Gas Furnace Electric Igniter Works

Electric igniters replace pilot lights by producing either heat or spark to light the gas burner. The furnace control board sends power to the igniter after a call for heat and after the inducer/blower and safety checks complete. When the igniter reaches operating temperature or produces a spark, the gas valve opens and burners ignite. The flame sensor or heat detection system verifies combustion and signals the control board to continue operation.

Main Types Of Electric Igniters

There are three primary electric igniter types commonly used in residential gas furnaces: hot surface igniters (HSI), spark igniters, and intermittent pilot systems that use an electric pilot assembly with a flame sensor. Each type operates differently and requires specific troubleshooting and replacement methods.

Hot Surface Igniter (HSI)

HSIs are made from silicon carbide or silicon nitride and glow red-hot when energized to ignite the gas. They are common in modern furnaces because they are quiet and reliable. HSIs are sensitive to mechanical damage and thermal cycling and often fail due to surface cracks or gradual degradation.

Spark Igniter

Spark igniters create an electrical arc across electrodes to ignite the gas. They resemble a small spark plug assembly and are favored in some designs for longevity and tolerance to thermal stress. Spark systems depend on a functioning ignition control module and properly spaced electrodes.

Intermittent Pilot And Pilot Ignition Assemblies

Some furnaces use a small, electrically controlled pilot that lights only when the furnace calls for heat. These systems include a pilot burner, electrode, and flame sensor. The pilot reduces standing pilot gas waste but requires a robust control sequence and reliable sensor feedback.

Common Symptoms Of A Failing Electric Igniter

Recognizing early warning signs of igniter problems can prevent complete furnace failure and improve safety. Common symptoms include the furnace attempting to ignite but failing, visible cracks on an HSI, repeated lockouts, extended ignition times, a clicking noise with no flame, and intermittent operation.

HSI-Specific Signs: No glow, visible damage, or delayed glowing before the gas valve opens.

Spark-Igniter Signs: Audible clicking with no spark or inconsistent sparking, electrode erosion or carbon buildup.

Control-Related Signs: Fault codes on the furnace control board, repeated ignition attempts, or complete lack of response point to controls, wiring, or safety interlocks.

Basic Troubleshooting Steps Homeowners Can Try

Before calling an HVAC technician, a few safe checks can clarify the issue. Always turn off power to the furnace at the service switch and breaker before inspecting internal components. If uncomfortable or unfamiliar with electrical work, contact a professional.

• Check Power And Thermostat: Confirm the thermostat calls for heat and the furnace has power. Replace thermostat batteries if applicable.
• Inspect Error Codes: Many modern furnaces flash an LED error code on the control board. Note the flash pattern and consult the furnace manual for interpretation.
• Look For Visible Damage: With power off, inspect the igniter for cracks, chips, or heavy deposits. HSIs often show visible cracks before failure.
• Check Flame Sensor Condition: A dirty flame sensor can cause repeated lockouts. Cleaning with a fine abrasive pad can restore reliable sensing.
• Verify Wiring And Connections: Loose, corroded, or burnt connectors between the control board and igniter can interrupt ignition.

When To Replace The Igniter Versus Repairing Components

If the igniter shows physical damage, fails electrical tests, or has exceeded expected lifespan, replacement is usually the best option. If the igniter looks intact but the furnace still fails to ignite, further diagnosis of the control board, gas valve, flame sensor, limit switches, and safety interlocks is needed.

Replace The Igniter When: Visible cracks exist, no resistance reading for HSI, or repeated failures tied to the igniter.

Repair Other Components When: Error codes point to gas valve malfunction, control board fault, or wiring issues. These components can often be repaired or replaced individually.

How Technicians Test Electric Igniters

Professional HVAC technicians use multimeters, ohmmeters, and observation to test igniters. An HSI typically shows a low resistance value when cold (check the manufacturer’s spec). An open circuit indicates a failed HSI. Spark systems require observation of spark gap activity and voltage output from the ignition module.

Technicians will also use visual inspections, flame rectification testing for flame sensors, and gas pressure checks to ensure the ignition event can support combustion once the igniter functions correctly.

Step-By-Step Replacement Process For A Hot Surface Igniter

Replacement steps are summarized here for informational purposes; homeowners should only attempt replacements if confident in electrical safety and furnace disassembly. When in doubt, hire a licensed technician.

1. Turn Off Power And Gas: Kill power at the breaker and switch off the gas supply.
2. Access The Burner Compartment: Remove the furnace access panels per the manufacturer instructions.
3. Disconnect Igniter Wires: Carefully disconnect the plug or terminal connectors from the igniter.
4. Remove Mounting Screws: Unscrew the igniter bracket and gently remove the igniter without touching the element surface.
5. Install New Igniter: Fit the replacement igniter in the same orientation, secure fasteners, and reconnect wiring.
6. Restore Power And Test: Turn power and gas back on, set the thermostat, and observe the ignition sequence for proper operation.

Cost Considerations And Lifespan

Igniter replacement costs vary by type and model. Typical parts and labor ranges in the U.S. are:

• HSI Replacement: $100–$300 installed depending on furnace access and part cost.
• Spark Igniter Replacement: $150–$350 installed, including ignition module checks.
• Intermittent Pilot Components: $150–$400 depending on assembly complexity.

HSIs generally last 3–5 years, spark systems can last longer but depend on electrode wear and control module longevity. Regular maintenance can extend service life.

Safety Tips And Best Practices

Working on gas furnaces involves risks from gas leaks, electrical shock, and scalding. Observe these safety precautions:

• Always turn off power at the breaker before servicing internal components.
• Shut off the gas supply before working on ignition or gas valves.
• Do not touch an HSI element with bare hands; oils from skin shorten its lifespan. Use gloves or a clean cloth.
• If a gas smell exists, evacuate the area, avoid using electrical switches, and call the gas utility and a licensed technician immediately.

Maintenance To Prevent Igniter Failures

Regular furnace tune-ups reduce ignition issues. Recommended maintenance tasks include filter replacement every 1–3 months, annual professional inspections, cleaning the flame sensor and burners, and checking electrical connections for corrosion or looseness.

Seasonal Checks: Before the heating season, run the furnace through several cycles to catch slow-to-ignite conditions and inspect the venting system for blockages.

Common Myths And Misconceptions

Several misconceptions circulate about electric igniters. Clearing these helps homeowners make informed decisions.

• Myth: HSIs last the life of the furnace. Reality: HSIs are consumable parts with a finite lifespan and thermal stress limits.
• Myth: Repeated cycling always means an igniter needs replacement. Reality: Control board faults, gas pressure issues, and dirty flame sensors can mimic igniter failure.
• Myth: Any igniter can be installed in any furnace. Reality: Igniters must match furnace model specifications for voltage, mounting, and resistance characteristics.

Choosing A Replacement Igniter

Select replacement parts based on the furnace model number, original equipment specifications, and OEM part numbers when possible. Universal igniters exist but may require adapters and careful matching of electrical characteristics.

When purchasing, verify the igniter’s voltage rating, mounting style, and connector type. Using OEM or high-quality aftermarket parts improves reliability and warranty coverage.

When To Call A Professional

Contact a licensed HVAC technician for complex diagnostics, gas valve issues, control board failures, persistent lockouts, or when the homeowner is uncomfortable performing electrical work. Professionals can perform safe gas pressure tests, advanced electrical diagnostics, and ensure code-compliant repairs.

Frequently Asked Questions

How Long Should An Electric Igniter Last?

Typical lifespans: HSIs 3–5 years, spark systems often longer. Lifespan depends on cycle frequency, operating conditions, and maintenance.

Can A Dirty Flame Sensor Prevent Ignition?

A dirty flame sensor can cause the control board to shut off the gas shortly after ignition, leading to repeated ignition attempts and lockouts. Cleaning the sensor often restores normal operation.

Is It Safe To Replace An Igniter Myself?

It can be safe if the homeowner is experienced with basic electrical safety, follows manufacturer instructions, turns off power and gas, and avoids touching the igniter element. If unsure, hire a licensed technician.

Why Does The Furnace Click But Not Ignite?

Clicking without ignition can indicate a failed spark igniter, compromised ignition module, blocked gas supply, or a gas valve issue. Professional diagnosis is advised if basic checks do not fix the problem.

Resources And Further Reading

For model-specific guidance, consult the furnace owner’s manual, the manufacturer’s technical documents, or reputable HVAC industry resources such as AHRI and ACCA. Homeowners should rely on licensed local HVAC contractors for installations and gas-related repairs.