How to Relight and Troubleshoot a Furnace Pilot Light

The pilot light on a gas furnace is a small flame that ignites the main burner and keeps the heating system operating safely. This article explains how a pilot light works, common reasons it goes out, step-by-step relighting procedures, key safety precautions, troubleshooting of related components like the thermocouple, and when to contact a qualified HVAC technician. It also covers preventive maintenance to reduce outages and improve efficiency.

Issue	Possible Cause	Quick Fix
Pilot Light Out	Draft, dirt, or gas supply	Relight, clear drafts, check gas
Pilot Won’t Stay Lit	Faulty Thermocouple	Replace thermocouple
Weak Pilot Flame	Clogged orifice or low gas pressure	Clean orifice, call utility
Strong Smell Of Gas	Gas Leak	Evacuate and call gas company

How A Furnace Pilot Light Works

The pilot light is a continuously burning flame that ignites the furnace’s main burners when the thermostat calls for heat. Most older or some standing-pilot furnaces use this design. A thermocouple or thermopile senses the pilot flame and signals the gas valve to remain open. If the flame goes out, the thermocouple cools and the gas valve shuts off to prevent unburned gas from accumulating.

Safety Precautions Before Working With A Pilot Light

Working with gas appliances involves risk. Always prioritize safety: turn off the furnace power if accessible, shut the gas valve to the appliance if you smell gas, and ensure adequate ventilation. Never attempt ignition if a strong gas odor is present; leave the area and call the gas company or 911 if required.

Personal Protective Measures

Wear safety glasses and avoid loose clothing. Keep a fire extinguisher rated for gas fires nearby. Have a phone and flashlight on hand. Ensure children and pets are kept away during any maintenance.

Common Reasons A Pilot Light Goes Out

Identifying the cause helps prevent repeat outages. Common causes include: drafts from open windows, doors, or leaky ducts; a dirty or clogged pilot orifice; a weak gas supply or low pressure; a failing thermocouple; or frequent cycling caused by a malfunctioning gas valve or thermostat.

Environmental And Mechanical Causes

Drafts and air movement can blow out a small pilot flame. Dust, spider webs, or debris near the pilot assembly can weaken the flame. Mechanical wear or corrosion of the thermocouple reduces its ability to sense heat reliably.

Step-By-Step: How To Safely Relight A Furnace Pilot Light

Only relight the pilot when there is no strong odor of gas and it is safe to do so. Follow the furnace manufacturer’s directions found on the furnace access panel or in the manual for model-specific steps.

Preparation

Turn off the thermostat and any power switch labeled “furnace” or “heater.” Locate the gas shutoff valve on the furnace and confirm it is open. Allow any residual gas to dissipate for at least five minutes if a smell was present earlier.

Relighting Procedure For Most Furnaces

1. Find the pilot access panel and remove it.
2. Set the gas control knob to “pilot” and press it in while holding a lighter or match near the pilot opening. Many furnaces require pressing the knob for 30 to 60 seconds to heat the thermocouple.
3. Release the knob and verify the pilot stays lit. If it extinguishes immediately, repeat the process once or refer to troubleshooting steps below.

Use a long fireplace lighter for safe ignition. For furnaces with an electronic ignition and no standing pilot, relighting is not applicable; instead, check ignition system diagnostics or call a technician.

Troubleshooting When The Pilot Light Won’t Stay Lit

If the pilot lights but goes out shortly after releasing the control knob, a thermocouple is the most common culprit. The thermocouple must be properly positioned in the flame and generate adequate millivolts to keep the gas valve open.

Thermocouple Inspection And Replacement

Visually inspect the thermocouple for soot, corrosion, or broken wires. Ensure the tip is properly immersed in the pilot flame. Clean gently with fine sandpaper if dirty. If cleaning doesn’t help, replacing the thermocouple is a straightforward and inexpensive repair for most DIYers comfortable with basic tools; otherwise hire a pro.

Pilot Orifice Cleaning

A weak flame can indicate a clogged pilot orifice. Turn off the gas, remove the pilot tube per manufacturer guidance, and clear the orifice with compressed air or a fine wire if accessible. Exercise caution and consult the manual, as orifice damage or improper reassembly can create hazards.

Gas Supply And Pressure Issues

Low gas pressure from the service line or a partially closed gas valve can weaken the pilot. Verify the main gas valve to the furnace is fully open. If the home’s gas appliances all show low flame, contact the gas utility to inspect pressure and regulator function.

When The Pilot Light Burns Yellow Or Soots

A healthy pilot flame is typically blue with a small inner cone. A yellow or sooty flame indicates incomplete combustion from dirt, improper air mixture, or venting problems. This condition reduces efficiency and may produce carbon monoxide.

Actions For Discolored Flames

Turn off the furnace and clean the pilot assembly. Check ventilation pathways and exhaust vents for blockages. If soot persists or there are signs of combustion problems, schedule a professional inspection and carbon monoxide testing.

Electronic Ignition Systems Versus Standing Pilot

Many newer furnaces use electronic ignition systems (hot surface igniters or intermittent pilots). These systems eliminate a continuously burning pilot and improve efficiency but require different troubleshooting. For electronic ignition faults, check diagnostic lights or error codes on the furnace control board and consult a technician for component-level repairs.

Preventive Maintenance To Keep The Pilot Light Reliable

Regular maintenance reduces pilot outages and extends furnace life. Have the furnace inspected annually by an HVAC technician, preferably before heating season. Basic homeowner tasks include keeping the area around the furnace clean and ensuring good ventilation.

Recommended Maintenance Tasks

• Replace air filters every 1–3 months during use to improve draft and combustion.
• Keep the furnace room free of dust, flammable materials, and strong drafts.
• Service the pilot assembly and burners annually to remove dirt and ensure correct flame shape.
• Test carbon monoxide detectors monthly and replace batteries yearly.

When To Call A Professional

If the pilot light repeatedly goes out, there is a gas odor, the pilot flame looks abnormal after cleaning, or a homeowner is uncomfortable working on gas appliances, contact a licensed HVAC technician. For electrical ignition or control board issues, a professional diagnosis ensures safe and correct repairs.

Finding A Qualified Technician

Look for technicians with state HVAC licenses, positive local reviews, and certifications from organizations like HVAC Excellence or NATE. Ask for written estimates and inquire about parts warranties and labor guarantees.

Cost Estimates For Common Repairs

Thermocouple replacement typically costs between $75 and $200 including parts and labor. Cleaning a pilot orifice may be included in a standard furnace tune-up costing $100 to $300. Major gas valve or control board replacements can range from several hundred to over a thousand dollars depending on parts and labor.

Signs Of Serious Problems And Carbon Monoxide Awareness

Any signs of yellow flames, soot buildup, persistent pilot outages, or unexplained health symptoms like headaches or dizziness warrant immediate attention. Install and maintain carbon monoxide detectors near sleeping areas and outside the furnace room. If a detector alarm sounds, evacuate and call emergency services.

Energy And Efficiency Considerations

A continuously burning pilot light consumes a small but constant amount of gas. Modern furnaces with electronic ignition improve efficiency by eliminating the pilot flame. Consider replacing an older standing-pilot furnace if frequent pilot issues persist or efficiency is a concern, balancing replacement cost against long-term energy savings.

Quick Troubleshooting Checklist

Symptom	Possible Fix
Pilot Out	Relight per instructions; check for drafts
Pilot Lights Then Goes Out	Inspect/replace thermocouple
Weak Flame	Clean orifice; verify gas pressure
Yellow Flame/Soot	Clean assembly; check venting; call pro
Strong Gas Smell	Evacuate; call gas company

Key Takeaways For Homeowners

Proper handling of a furnace pilot light involves safe relighting procedures, awareness of thermocouple and orifice issues, and attention to gas supply and venting. Safety is paramount: never ignore the smell of gas or persistent combustion irregularities. Regular maintenance and timely professional service keep the furnace operating safely and efficiently.

Helpful Resources And References

Recommended references include the furnace manufacturer’s owner manual, the U.S. Consumer Product Safety Commission guidance on gas appliances, and local gas utility safety information. For technical repairs, refer to licensed HVAC professionals and certified technicians for diagnostics and replacement parts.