Furnace Ignitor Lights Then Goes Out: Causes and Fixes

The common problem where a furnace ignitor lights then goes out can leave homeowners cold and confused. This article explains why the ignitor lights then goes out, identifies likely causes, and outlines step-by-step troubleshooting and repair options for U.S. residential furnaces. It focuses on safety, efficiency, and clear next steps for HVAC technicians or informed homeowners.

Symptom	Likely Cause	Immediate Action
Ignitor Lights Then Goes Out	Faulty flame sensor, dirty burners, weak gas supply, control board issue, or pressure switch problem	Turn off power; inspect flame sensor and burners; call HVAC if unsure

How A Furnace Ignitor System Works

A basic understanding of the furnace ignition sequence helps identify why the ignitor lights then goes out. Modern gas furnaces use an electronic ignitor or hot surface ignitor (HSI) to create ignition instead of a pilot light. The control board energizes the ignitor, the gas valve opens, and burners should light and remain lit after the flame is verified.

The control board monitors input from sensors like the flame sensor and pressure switch. If the control board detects no sustained flame within a predefined period, it shuts the gas valve and turns off the ignitor to prevent unburned gas buildup. This safety-driven shutdown is the core reason an ignitor lights then goes out.

Common Causes When Ignitor Lights Then Goes Out

1. Faulty Or Dirty Flame Sensor

The flame sensor verifies that burners are producing a flame. If contaminated by soot or oxidation it can fail to sense flame quickly or reliably. A malfunctioning flame sensor commonly causes the system to shut off gas after the ignitor lights then goes out.

2. Weak Or Intermittent Gas Supply

If gas pressure is too low, burners may not sustain a flame. Gas valves, regulators, or supply lines with partial obstructions can allow ignition but fail to produce consistent flame, causing the ignitor to extinguish after lighting.

3. Dirty Or Misaligned Burners

Burner ports clogged with debris or misaligned burners produce unstable flames. A burner that lights briefly then collapses will trigger the control board to shut down the system. Burner condition is a frequent, fixable cause.

4. Faulty Ignitor Or Ignitor Wiring

Although the ignitor itself lights briefly, a failing ignitor element or intermittent wiring can cause inconsistent ignition timing and premature shutdowns. Cracked ceramic or degraded wiring increases resistance and can cause erratic behavior.

5. Pressure Switch Or Venting Issues

The pressure switch verifies that the inducer motor and venting are functioning before allowing ignition. If the inducer fails to reach correct vacuum or venting is blocked, the control board may allow a short ignition but then close down for safety.

6. Control Board Or Relay Malfunction

Control boards time the ignition sequence and process sensor feedback. A defective board or failing relay might incorrectly interpret sensor inputs or prematurely cut power to the gas valve after a brief ignition.

7. Thermostat Or Wiring Problems

A thermostat sending erratic calls for heat or wiring shorts can interrupt the ignition sequence. If the thermostat stops calling for heat after the ignitor lights, the furnace will shut down the flame and ignitor.

Diagnostic Checklist: Step-By-Step Troubleshooting

Follow safety-first diagnostics. Turn off power and gas before any internal inspection. If the homeowner is not comfortable, contacting a licensed HVAC technician is recommended.

1. Observe The Sequence: Turn the thermostat up, watch the furnace cycle and note exact behavior and error codes on the furnace control board if available.
2. Check Error Codes: Many furnaces flash LED codes. Photograph the pattern and consult the manual to map the code to likely failures.
3. Inspect Flame Sensor: Access the flame sensor, remove it, and clean the metal rod gently with fine-grit sandpaper or steel wool. Reinstall and retest.
4. Examine Burners: Check for rust, debris, or misalignment. Clean burner ports with a soft brush and compressed air if required.
5. Test Gas Pressure & Valve: A qualified technician should measure inlet pressure and confirm the gas valve functions under load.
6. Check Ignitor & Wiring: Inspect ignitor for cracks and test resistance with a multimeter if trained to do so. Replace a visibly damaged ignitor.
7. Evaluate Inducer & Pressure Switch: Verify inducer motor operation and hose connections. Test the pressure switch for proper continuity when the inducer runs.
8. Inspect Control Board & Relays: Look for burnt components, swollen capacitors, or cold solder joints. Replace the board if diagnostics and symptoms point to failure.
9. Verify Thermostat: Test for continuous call for heat during ignition cycle. Swap or bypass thermostat if needed to rule it out.

Cleaning And Simple Repairs Homeowners Can Do

Some maintenance tasks safely performed by homeowners may resolve the ignitor lights then goes out problem. Always disconnect power to the furnace before accessing internal parts.

• Clean The Flame Sensor: Remove and wipe the sensor with fine sandpaper and reassemble for immediate improvement.
• Clean Burners And Orifices: Vacuum dust from around burners and use a brush to remove debris from ports without bending them.
• Replace Air Filters: Restricted airflow can affect burner performance indirectly; install a fresh furnace filter and ensure vents are open.
• Check Vent Pipes: Inspect exterior vent termination for blockages from nests or debris and clear as needed.

When To Call A Professional HVAC Technician

Call a licensed HVAC technician when the problem involves gas pressure, control board replacement, inducer motor repair, or when in doubt. Working on gas valves and pressure components can be dangerous and may void warranties if performed by unqualified individuals.

Situations Requiring Professional Help: Persistent shutdowns after cleaning, smell of gas, inability to measure correct gas pressure, recurring control board error codes, or multiple component failures.

Replacement Parts And Costs

Costs vary by region and furnace model. Typical U.S. price ranges include flame sensor replacement from $50 to $150 for parts and labor, ignitor replacement from $100 to $350, and control board replacement from $300 to $800. Labor rates and part complexity can shift these ranges.

Part	Typical Cost Range (Parts + Labor)
Flame Sensor	$50 – $150
Ignitor	$100 – $350
Control Board	$300 – $800

Prevention And Routine Maintenance

Regular maintenance reduces the chance the ignitor lights then goes out. Schedule annual HVAC tune-ups before heating season and perform basic tasks periodically.

• Annual Professional Tune-Up: Include burner inspection, ignition system check, gas pressure test, and safety control verification.
• Quarterly Filter Changes: Replace or clean filters to maintain airflow and combustion stability.
• Keep Vents Clear: Ensure household vents and outside exhaust terminations are unobstructed.
• Monitor For Early Signs: Note unusual cycling, strange odors, or intermittent operation and address quickly.

Troubleshooting Table: Symptoms, Causes, And Actions

Symptom	Possible Cause	Action
Ignitor Lights, No Flame Holds	Dirty flame sensor	Clean sensor and retest
Ignitor Lights, Flame Flickers Then Extinguishes	Low gas pressure or clogged burners	Call technician to test gas pressure and clean burners
Ignitor Lights Then Goes Out With Error Code	Control board or pressure switch fault	Record code and contact HVAC pro
Ignitor Lights Then Goes Out Occasionally	Intermittent wiring or thermostat issue	Inspect wiring, replace thermostat batteries, or swap thermostat

Safety Tips And Gas Leak Awareness

If a homeowner smells gas, evacuate immediately and call the gas company or emergency services. Do not operate electrical switches or the furnace. A persistent gas odor, hissing sound near the gas line, or visible corrosion on fittings warrants urgent professional intervention.

Additional Safety Advice: Keep carbon monoxide detectors installed near sleeping areas and replace batteries annually. Ensure the furnace area remains free of flammable materials.

FAQ: Quick Answers To Common Questions

Why Does The Ignitor Light But The Burners Don’t Stay Lit?

Commonly caused by a dirty flame sensor, low gas pressure, or clogged burners. The control board will shut off gas if flame isn’t detected consistently.

Can Cleaning The Flame Sensor Fix The Problem?

Yes, cleaning the flame sensor often resolves the issue when the sensor is contaminated. It is a low-cost first step before replacing parts.

Is It Safe To Replace The Ignitor At Home?

Replacing an ignitor is doable for handy homeowners if the furnace is powered off and the correct replacement is used. If uncertain, hire a professional to avoid breakage or electrical issues.

How Long Should An Ignitor Last?

Hot surface ignitors typically last 3–7 years depending on usage and quality. Frequent cycling or power surges can shorten lifespan.

Resources And References

Reliable sources for further reading include manufacturer manuals for common furnace brands, the U.S. Consumer Product Safety Commission for carbon monoxide guidance, and EPA recommendations on indoor air quality. For model-specific wiring diagrams, consult the furnace’s service manual or the manufacturer’s technical support.

If the ignitor lights then goes out after these checks, document observations and error codes before contacting an HVAC technician to expedite diagnosis and repair.