Why Your Furnace Pilot Light Keeps Going Out and How to Fix It

The pilot light on a gas furnace that keeps going out is a common and potentially hazardous problem that affects comfort, safety, and energy efficiency. This article explains the likely causes, safe troubleshooting steps, maintenance tips, and when to call a professional to ensure reliable heating. Key takeaway: many pilot issues are fixable, but persistent outages warrant professional inspection for safety reasons.

Symptom	Common Causes	Quick Fix
Pilot extinguishes frequently	Draft, dirty pilot, faulty thermocouple	Clean pilot area, check for drafts, replace thermocouple
Pilot won’t stay lit after lighting	Faulty gas valve, weak gas pressure, bad thermocouple	Test gas flow, call HVAC tech
Pilot difficult to light	Clogged orifice, air in gas line	Clean orifice, purge line, professional service

How The Furnace Pilot Light Works

The pilot light is a small, steady flame that ignites the furnace’s main gas burner. Older furnaces use a continuously burning pilot; many modern units use an electronic ignition or hot surface igniter instead. A mechanical pilot system includes a pilot orifice, thermocouple (or thermopile), gas control valve, and safety switches.

The thermocouple is a temperature-sensing device that tells the gas valve to stay open when the pilot flame is hot. If the flame goes out, the thermocouple cools and signals the valve to shut off gas flow, preventing leaks. Problems with any of these components or with gas supply and airflow can cause the pilot light to go out.

Common Causes For A Pilot Light That Keeps Going Out

Poor Drafts Or Airflow

Strong drafts near the furnace, wind-driven chimney drafts, or improper venting can blow out the pilot flame. Negative pressure in the home caused by exhaust fans or tightly sealed homes with inadequate combustion air can also snuff the pilot.

Dirty Or Clogged Pilot Orifice

Over time dust, soot, or spider webs can clog the pilot orifice or pilot tube, reducing flame strength and stability. A weak flame is more likely to be extinguished by minor disturbances.

Faulty Thermocouple Or Thermopile

A worn, bent, or coated thermocouple may not register enough heat to keep the gas valve open. Thermopiles used with millivolt gas valves can degrade, producing insufficient voltage to operate the valve reliably.

Gas Supply Issues

Low gas pressure, debris in the gas line, or a partially closed gas valve can reduce flame size. Intermittent gas supply can make the pilot hard to light or keep lit.

Malfunctioning Gas Control Valve Or Safety Switch

Gas control valves can fail mechanically or electrically. Safety features like flame rollout switches, limit switches, or pressure switches may open and shut off gas delivery if they detect unsafe conditions.

Thermostat Or Wiring Problems

In some systems, faulty wiring or controls can prevent proper ignition sequences. This is less common with simple pilot systems but can affect ignition in more modern setups.

Corroded Or Damaged Components

Corrosion, loose connections, or mechanical damage to pilot assembly parts can interfere with flame stability. Age-related wear often contributes to repeated pilot outages.

Safe Troubleshooting Steps Homeowners Can Try

Important Safety Note

Working with gas appliances carries risks. If a homeowner smells gas strongly, evacuate, avoid switches or flames, and call the gas company or emergency services. If unsure about any repair, contact a licensed HVAC or gas technician.

Check For Drafts And Venting Issues

Inspect around the furnace and chimney for open windows, vents, or strong airflow sources. Temporarily close nearby windows and turn off large exhaust fans to see if the pilot stays lit. Ensure the furnace room has adequate combustion air.

Examine And Clean The Pilot Assembly

Turn off the gas and power to the furnace before cleaning. Use compressed air or a soft brush to remove dust and debris from the pilot orifice and pilot tube. Do not use metal tools that could enlarge the orifice. After cleaning, relight according to the manufacturer’s instructions.

Inspect The Thermocouple

Visually inspect the thermocouple for soot, bends, or loose connections at the gas valve. Carefully clean soot buildup with fine emery cloth and ensure the thermocouple tip sits securely in the pilot flame. If cleaning doesn’t help, replacement is inexpensive and a common fix.

Verify Gas Supply And Valve Position

Confirm the gas shutoff valve at the furnace is fully open. If using LP (propane), ensure the tank has adequate pressure. If the pilot barely ignites or gas odor exists, contact the gas utility or a professional.

Test And Replace The Thermocouple Or Thermopile

For those comfortable with basic tools, thermocouple output can be tested with a multimeter, or simply replaced as a troubleshooting step. Replacement typically requires unscrewing the old sensor and installing a compatible new one. After replacement, retest pilot operation.

Check For Loose Connections And Corrosion

Inspect visible wiring, connectors, and the gas valve area for corrosion or looseness. Tighten connections as needed after turning power off. Corroded components may need professional replacement.

When To Call A Professional

Call a licensed HVAC technician or gas fitter if the pilot light continues to go out after basic cleaning and thermocouple replacement, if gas odor is present, or if ignition sequences or control components appear faulty.

Complex issues requiring professional service include: defective gas control valves, internal gas line blockages, chimney or venting repairs, pressure switch or safety control failures, and suspected carbon monoxide problems.

Safety Precautions And Carbon Monoxide Awareness

A malfunctioning furnace can produce carbon monoxide (CO). Install and maintain CO detectors near sleeping areas and the furnace. If a CO alarm sounds, exit immediately and call emergency services.

Never seal combustion air openings in the furnace room, and do not operate a furnace with known venting or combustion issues. Regular safety inspections by a qualified technician are essential for older units.

Preventive Maintenance To Keep The Pilot Stable

• Annual Professional Tune-Up: Schedule a yearly HVAC inspection including pilot, burner, heat exchanger, and venting checks.
• Filter Replacement: Replace air filters regularly to reduce dust that can travel to the pilot assembly.
• Keep Area Clean: Maintain a clean furnace area free of debris, pests, and combustible materials.
• Combustion Air: Ensure proper combustion air supply, especially in tightly sealed homes; consider passive vents if required.
• Monitor Thermocouple Age: Replace thermocouples that show wear; they are low-cost and prevent recurring outages.

Cost Estimates For Common Repairs

Costs vary by region, but general ranges in the U.S. are:

• Thermocouple replacement: $75–$200 including parts and labor.
• Pilot orifice cleaning: $50–$150 if performed by a technician, less if DIY.
• Gas control valve replacement: $300–$800+ depending on furnace model.
• Annual tune-up: $100–$200.

Always request a written estimate and verify technician licensing and insurance before work begins.

Signs That The Furnace Needs Replacement

While pilot issues are often repairable, repeated failures combined with other problems may indicate an aging furnace that should be replaced. Consider replacement when the furnace is over 15–20 years old, experiences frequent breakdowns, has a cracked heat exchanger, or operates inefficiently.

Upgrading to a modern high-efficiency furnace with electronic ignition eliminates a standing pilot light and reduces energy waste, improving safety and lowering operating costs.

Frequently Asked Questions

Why Does The Pilot Keep Going Out Only When The Wind Blows?

Exterior wind can create negative pressure in the chimney or around vents, drawing the pilot flame away. Proper draft diverters, vent caps, or adjusting chimney termination can reduce wind-related outages.

Is It Safe To Relight The Pilot Myself?

Relighting is safe when following the manufacturer’s procedure and when no gas odor exists. If the pilot requires repeated relighting, stop attempting and call a technician due to potential underlying gas or safety issues.

Can A Dirty Furnace Cause The Pilot To Go Out?

Yes. Dust, soot, and debris can clog the pilot orifice and reduce flame strength. Regular cleaning and filter changes reduce this risk.

How Long Does A Thermocouple Last?

Thermocouples often last several years but can fail sooner from corrosion, soot buildup, or mechanical stress. They are inexpensive to replace and are a common solution for pilot outages.

Useful Checklist Before Calling A Technician

1. Check for gas odor and evacuate if present.
2. Confirm the furnace gas valve is open.
3. Look for drafts or open windows near the furnace.
4. Change or inspect the air filter.
5. Clean the pilot area and inspect the thermocouple.
6. Note when the pilot goes out and any accompanying patterns or noises.

Providing these details to a technician can speed diagnosis and reduce service time.

Final Note: While many homeowners can resolve simple pilot light problems, persistent outages or safety concerns require prompt professional attention. Proper maintenance and timely repairs preserve comfort, efficiency, and safety of the heating system.