Furnace Ignitor Not Glowing: Troubleshooting, Causes, and Fixes for Gas Furnaces

When a furnace ignitor is not glowing, the heat never starts—and winter gets uncomfortable fast. This guide explains how ignition works, the most common reasons an ignitor stays dark, safe DIY checks, and when to call a pro. It is tailored for U.S. homes and focuses on hot surface ignitors used in modern gas furnaces.

How A Gas Furnace Ignitor Works

Most modern furnaces use a hot surface ignitor (HSI), a small element that glows red-hot to ignite gas. It replaces old pilot lights and improves efficiency and safety. When the thermostat calls for heat, the control board powers a precise startup sequence.

The typical sequence: the inducer motor starts to move exhaust, the pressure switch confirms draft, the board energizes the ignitor at 120 VAC, the gas valve opens, flames ignite, the flame sensor proves flame, and the blower starts after a short delay.

If the furnace ignitor is not glowing, something has interrupted this sequence. The cause may be a failed ignitor, a safety switch, a blocked vent, a control board issue, or power problems. Correct diagnosis saves time and money.

Quick Checks Before You Dive In

Start with safe, simple steps that resolve many “furnace ignitor not glowing” cases. These checks avoid unnecessary parts replacement and ensure the system can run at all.

• Thermostat: Set to Heat, temperature above room level, and Fan set to Auto.
• Power: Confirm the furnace switch is on, the breaker is not tripped, and the front door panel is properly latched to engage the door safety switch.
• Filter: Replace a dirty filter; severe restriction can trip limit switches and halt ignition.
• Condensate: On high-efficiency furnaces, empty a full condensate pan, clear clogs, and ensure hoses are attached and not kinked.
• Intake/Exhaust: Check exterior PVC vent and intake for ice, leaves, or nests; clear blockages.
• Reset: Power off the furnace for 60 seconds, then restore power to reset a soft lockout.

Safety first: Turn off power before removing panels. Do not bypass safety switches or attempt gas repairs without proper training and tools.

Step-By-Step Troubleshooting When The Furnace Ignitor Is Not Glowing

Watch The Startup Sequence

Stand near the furnace and listen after a heat call. The inducer should start within seconds. Many control boards have an LED with blink codes. Check the legend on the panel door for code meanings. Lockout codes often signify a safety or sensor issue.

If The Inducer Does Not Start

No inducer means the board has not reached the ignitor step. Causes include loss of power, a tripped limit or rollout switch, a faulty inducer, or a bad control board. Check the breaker, door switch, and any manual reset rollout switches near the burners.

Blocked venting or a failed pressure switch can also keep the inducer from running or proving draft. On condensing units, a full condensate trap or blocked drain can interrupt the draft circuit. Clear drains and verify hoses are intact.

If The Inducer Runs But The Ignitor Stays Dark

This scenario is common. With the inducer running, the board should energize the ignitor. If the furnace ignitor is not glowing, suspect a failed ignitor, open safety circuit, loose harness, bad board, or incorrect polarity/neutral.

• Listen and look: After inducer starts, the ignitor should glow within 30–90 seconds depending on model.
• Check wiring: Inspect the ignitor’s connector and wires for cracks, burns, or loose pins. The ignitor is fragile—do not touch the element.
• Board fuse: Many boards have a 3–5 amp blade fuse. If blown, find and correct the short before replacing.
• Voltage check (advanced): During the heat call, a working board typically supplies ~120 VAC to the ignitor leads. Voltage present but no glow indicates a bad ignitor. No voltage suggests an open safety or failed board.

If The Ignitor Glows Then Goes Dark Quickly

If the ignitor glows but there is no flame, the gas may not flow. Causes include a closed gas valve, failed gas valve, no gas supply, or control board issues. If flame lights but drops out, a dirty flame sensor is common. While related, this situation differs from a completely dark ignitor.

Common Causes And How To Address Them

Multiple conditions can stop an ignitor from glowing. The list below maps likely causes to practical next steps. Address simple airflow and drain issues first before replacing parts.

• Cracked or burned-out hot surface ignitor: The most common failure. Look for hairline cracks or white deposits. If line voltage is present and no glow, replace the ignitor.
• Open limit or rollout switch: Overheating or flame rollout opens these safety switches. Inspect for blocked filters, closed vents, or blower issues. Some rollout switches are manual-reset; press the small button if present after resolving the cause.
• Faulty pressure switch or blocked venting: If draft is not proven, the board will not power the ignitor. Clear intake/exhaust obstructions, ensure the condensate trap is clean, and verify tubing connections.
• Loose or damaged ignitor harness: Heat and vibration can loosen connectors. Secure and reseat the plug; look for heat damage near the burners.
• Control board failure or blown board fuse: A bad relay or burnt trace can stop ignitor power. If the board does not output voltage during ignition, replacement may be required after ruling out safety circuits.
• Incorrect line polarity or missing neutral/ground: Some boards require proper hot-neutral orientation. Check outlets and wiring if the furnace was recently serviced or moved to a new circuit.
• Thermostat or low-voltage issues: Loose R-W connections, a broken thermostat wire, or a tripped transformer fuse can halt the sequence before ignition.
• Condensate float switch open: If present, a full condensate pan opens the circuit and blocks ignition. Empty the pan and clear the drain line.

DIY Fixes You Can Do Safely

Several actions are safe for most homeowners and often resolve a “furnace ignitor not glowing” issue without specialized tools. Avoid gas valve adjustments or bypassing any safeties.

• Replace the air filter: A clogged filter triggers high limits and prevents ignition. Use the correct size and MERV rating recommended by the manufacturer.
• Clear intake and exhaust pipes: Remove visible blockages, especially in freezing weather where ice can form at terminations.
• Empty and flush the condensate trap: For condensing furnaces, clean the trap and ensure the hose slopes to drain. Refill the trap with clean water to maintain the air seal.
• Reseat connectors: With power off, gently reseat the ignitor connector, pressure switch tubes, and the door switch plug.
• Clean the flame sensor (if flame drops after ignition): Not directly for a dark ignitor, but helpful if the system lights and then shuts down. Use a fine abrasive pad lightly; avoid touching the ceramic insulator.
• Power reset: Cycle power at the switch or breaker to clear a soft lockout after correcting issues.

Note: Replacing an ignitor is feasible for experienced DIYers, but the element is extremely fragile. If unsure, hire a licensed HVAC technician.

When To Call A Professional

Professional help is recommended when electrical diagnostics or gas handling is required. This ensures safety and avoids repeat failures due to misdiagnosis or improper parts.

• No 120 VAC to ignitor during the heat call: A pro can trace safeties, verify polarity, and test the control board.
• Repeated lockouts or flashing error codes: Indicates deeper issues like intermittent pressure switch operation or board faults.
• Inducer noise, seized motor, or vibration: Draft problems can cascade into ignition failure.
• Evidence of heat damage or rollout: Sooting, scorch marks, or tripped rollout switches require expert evaluation of the heat exchanger and venting.
• Gas supply or valve concerns: Leave gas pressure and valve tests to licensed technicians.

Maintenance To Prevent Ignitor Problems

Routine maintenance extends ignitor life and improves reliability. A clean, well-ventilated system reduces stress on the ignition and safety circuits, minimizing winter breakdowns.

• Annual professional tune-up: Includes combustion analysis, cleaning burners, checking safeties, and verifying venting and condensate drains.
• Quarterly filter checks: Replace filters more often in homes with pets or renovation dust.
• Keep vents clear: Maintain at least 12 inches of clearance around intake/exhaust terminations.
• Avoid touching the ignitor: Skin oils can create hot spots and premature failure.
• Verify drainage: Condensing furnaces need clear, sloped drains and a clean trap to avoid pressure switch trips.

Replacement Guide: Picking The Right Ignitor

Ignitors are not universal. Selecting the correct part prevents early failure and ensures proper ignition timing. There are two main types: silicon carbide and silicon nitride.

• Silicon carbide HSI: Common, cost-effective, and slightly more brittle. Usually shaped like a flat or spiral element.
• Silicon nitride HSI: More durable and resistant to thermal shock. Often rod-style or fork-style elements.
• Match specifications: Use the furnace model number or existing ignitor’s part number to source an exact or approved replacement.
• Bracket and connector: Some ignitors require a specific bracket or plug; adapter kits may be available.
• Handling: Avoid touching the element. Hold by the ceramic base and keep it clean and dry.

During replacement, cut power, remove the burner compartment door, and take photos of wire routing. After installation, restore power, call for heat, and watch for a steady glow followed by ignition.

Costs, Timelines, And What To Expect

Budgeting helps decide between DIY and professional service. Prices vary by brand, region, and furnace accessibility. The estimates below provide a general range for U.S. homeowners.

• Ignitor replacement: $80–$300 installed; parts typically $20–$80 for silicon carbide and $40–$120 for silicon nitride.
• Service call/diagnostic: $100–$200, often credited toward repairs.
• Pressure switch: $150–$350 installed depending on capacity and access.
• Control board: $400–$900 installed, heavily brand-dependent.
• Inducer motor assembly: $500–$1,200 installed due to parts and labor.

Simple ignitor swaps can take 30–60 minutes. Complex diagnostics involving draft, drainage, or controls may take longer. Ask for a written estimate and warranty on parts and labor.

Troubleshooting Cheatsheet

The table below summarizes common symptoms, likely causes, and what to check when the furnace ignitor is not glowing. Use it to prioritize quick wins and decide when to call a pro.

Technical Notes For Advanced DIYers

For those with electrical experience and proper tools, measured data can sharply narrow the issue. Always isolate power and follow safety best practices before testing.

• Ignitor resistance (cold): A reading that is open (infinite) indicates a failed element. Compare to manufacturer specifications for your part number.
• Ignitor voltage during call for heat: Expect approximately 120 VAC at the ignitor leads when the control board commands ignition.
• Safety circuit continuity: Series safeties (limit, rollout, pressure switch) must be closed for ignition. An open reading identifies the tripped device to investigate.
• Grounding and polarity: Incorrect neutral or ground can cause board errors and failed ignition. Verify outlet wiring if the furnace was recently serviced.

Warning: Do not bypass pressure switches, limits, or rollouts even for testing. These devices prevent dangerous conditions and must remain functional.

Why The Ignitor Fails Prematurely

Ignitors are consumables, but certain conditions shorten their life. Addressing root causes reduces repeat failures and keeps heat reliable throughout the season.

• Frequent cycling: Undersized thermostat cycles or oversizing can stress the ignitor. Consider thermostat settings that minimize short cycling.
• Vibration and shock: Handling or moving the element can crack it. Always hold by the ceramic base.
• Contamination: Dust, lint, and chemicals can coat the ignitor and create hot spots. Keep the furnace area clean and avoid aerosols nearby.
• High supply voltage or poor grounding: Electrical anomalies stress the element and control board. A pro can check supply quality.

How This Connects To Other Furnace Symptoms

A “furnace ignitor not glowing” problem often appears alongside other issues. Recognizing patterns helps pinpoint the cause faster and avoids unnecessary part swaps.

• Cold air from vents: The blower may run on a delay or purge cycle even when ignition fails, moving unheated air.
• Clicking sounds: The board may retry ignition several times, cycling relays and the inducer motor.
• Chemical or gas odor: If gas smell is present, shut off the gas supply, evacuate, and contact the gas utility immediately.
• Water near the furnace: On high-efficiency units, a blocked condensate line can prevent ignition and cause leaks.

SEO Tips: Matching Search Intent For “Furnace Ignitor Not Glowing”

Homeowners typically search this phrase during a no-heat event. They want quick checks, likely causes, costs, and whether the fix is DIY or professional. This article provides those answers with step-by-step guidance and safety notes.

• Related terms to know: hot surface ignitor, HSI, pressure switch, inducer motor, flame sensor, limit switch, control board.
• Action-oriented tips: Reset power, clear vents, replace filters, inspect condensate drains, and read LED codes before replacing parts.
• Decision clarity: If no 120 VAC to the ignitor or recurring lockouts, schedule professional service.

Frequently Asked Questions

Why Is My Furnace Ignitor Not Glowing At All?

The most common reasons are a failed ignitor, an open safety circuit like a limit or pressure switch, a blocked vent or drain, or a control board problem. Start with power, filter, vents, and condensate checks, then consider diagnostics or a service call.

How Long Should A Hot Surface Ignitor Last?

Many last 3–7 years, but life varies by cycling frequency, air quality, and part quality. Silicon nitride designs tend to last longer than silicon carbide, especially in systems that cycle frequently.

Can I Test An Ignitor With A Multimeter?

Yes. With power off and the connector unplugged, measure resistance across the ignitor leads. An open circuit indicates failure. During a heat call, a professional can test for about 120 VAC at the ignitor wires to confirm board output.

Is It Safe To Replace A Furnace Ignitor Myself?

Careful DIYers can replace an ignitor, but the element is fragile and the burner area is confined. Turn off power and let the furnace cool. If wiring, bracket alignment, or diagnostics are unclear, hire a licensed technician.

What If The Ignitor Glows But There’s No Flame?

That points to a gas supply or gas valve issue, or delayed timing from the control board. Confirm gas is on, and call a professional for valve and pressure tests. A dirty flame sensor causes flame dropout, not a dark ignitor.

Why Does My Furnace Keep Locking Out?

Lockouts occur after failed ignition attempts or safety trips. Common triggers include blocked vents, faulty pressure switches, dirty sensors, and control board faults. Clear obvious issues and reset power. Recurring lockouts need diagnosis by a pro.

Will A Dirty Filter Stop The Ignitor From Glowing?

Indirectly. A severely clogged filter can overheat the heat exchanger and open the high-limit switch. The control board then halts ignition to protect the system. Replacing the filter often restores normal operation.

How Do I Read Furnace Error Codes?

Most furnaces flash an LED on the control board. A legend on the blower or burner door explains the codes. Count the flashes, match them to the chart, and follow the suggested checks before replacing parts.

Key Takeaways For Fast Heat Recovery

When the furnace ignitor is not glowing, start with basics: thermostat, power, filter, vents, and drains. Watch the startup sequence and read error codes. If the inducer runs and there’s no ignitor glow, the ignitor or board output is suspect. For electrical or gas diagnostics, schedule a professional.

Keeping filters clean, vents clear, and drains flowing prevents many ignition issues. With smart checks and timely service, the furnace will light reliably and keep the home comfortable all season.