The pilot light plays a critical role in many gas furnaces, igniting the main burner to produce heat. This article explains how a pilot light functions, common problems, safe relighting procedures, and when to replace components or call a professional. It focuses on practical guidance for homeowners in the United States and highlights safety, code considerations, and modern alternatives.
| Topic | Quick Summary |
|---|---|
| What Is A Pilot Light | Small, continuous flame that ignites the furnace burner |
| Common Issues | Outage, weak flame, thermocouple failure, draft |
| Relighting | Follow manufacturer steps; ensure gas off and proper venting |
| Replacement/Upgrade | Thermocouple, pilot assembly, or switch to electronic ignition |
How A Gas Furnace Pilot Light Works
A pilot light is a small, continuously burning flame that lights the furnace’s main burners when the thermostat calls for heat. It is commonly found in older gas furnaces that use a standing pilot ignition system rather than electronic igniters. When the thermostat signals for heat, the gas valve opens to the main burners, and the pilot light ignites the flowing gas.
The pilot assembly typically includes a pilot orifice, pilot tube, thermocouple, and a flame sensor or pilot safety valve. The thermocouple detects heat from the pilot flame and allows the gas valve to stay open; if the flame goes out, the thermocouple cools and shuts off gas to prevent leaks.
Types Of Pilot Ignition Systems
Furnaces use either a standing pilot or an intermittent pilot/electronic ignition. Standing pilot systems maintain a continuous flame, consuming a small amount of gas constantly. Electronic ignition systems eliminate the standing pilot by using a spark or hot surface igniter, improving efficiency and reducing gas use.
| System | Key Features | Pros | Cons |
|---|---|---|---|
| Standing Pilot | Continuous flame, thermocouple safety | Simple, reliable start | Constant gas usage, higher energy cost |
| Intermittent Pilot | Pilot ignites only when needed | Lower gas use than standing pilot | More components, electronic control |
| Electronic Ignition | Spark or hot surface igniter | High efficiency, no pilot gas loss | Higher initial cost, electronic fail points |
Common Pilot Light Problems And Causes
Pilot light problems often present as the furnace failing to heat, the pilot being out repeatedly, or a weak/yellow flame. Typical causes include drafts, clogged pilot orifice, faulty thermocouple, improper gas pressure, and build-up of dirt or corrosion.
A yellow or flickering flame can indicate incomplete combustion, which raises carbon monoxide risk. A healthy pilot flame is usually steady and blue with a small inner cone; any deviation warrants inspection and possible professional service.
Safe Steps To Relight A Pilot Light
Relighting a pilot should follow the furnace’s manufacturer instructions printed on the unit. If directions are missing, use a typical safe procedure: shut off the gas and power, wait five minutes for gas to dissipate, turn the gas control knob to “pilot,” depress and hold the knob while lighting, then hold the knob for 30–60 seconds after ignition, and finally set the control to “on.”
Before relighting, check for gas smell. If gas is smelled strongly, evacuate the area and call the gas company or emergency services. Also confirm that venting is unobstructed and carbon monoxide detectors are functioning.
Thermocouple And Flame Sensor Issues
The thermocouple and flame sensor are safety devices that detect the pilot or main flame. A failing thermocouple typically causes the pilot to light but not stay lit, because it fails to signal the gas valve to remain open. Cleaning the thermocouple or sensor can help, but replacement is often required when wear or corrosion is present.
To test a thermocouple, a professional will measure voltage output when heated; values below specifications indicate replacement. Flame sensors on electronic ignition systems require similar maintenance and occasional replacement to ensure reliable operation.
Troubleshooting Checklist For Homeowners
- Verify thermostat settings and power to the furnace.
- Look for error codes on modern units or indicator lights.
- Inspect the pilot flame for color and stability.
- Check for drafts, open windows, or vents near the pilot assembly.
- Clean the pilot orifice with compressed air or a thin wire if accessible.
- Ensure the gas supply valve to the furnace is open.
- Test or replace the thermocouple if the pilot will not stay lit.
- Call a licensed technician for ignition module or gas valve issues.
When To Call A Professional
Homeowners should contact a licensed HVAC or gas technician for repeated pilot outages, suspected gas leaks, yellow burner flames, smell of gas, or if the homeowner is uncomfortable performing relighting or maintenance. Technicians have the tools and training to test gas pressure, inspect the burner assembly, and safely repair or replace gas valves and ignition components.
Code and permit issues may apply to furnace repairs in some jurisdictions; a licensed contractor ensures compliance with local building and safety codes.
Replacing Pilot Components And Costs
Common replacement parts include thermocouples, pilot assemblies, gas valves, and electronic ignition modules. Thermocouples are relatively inexpensive and can range from $20 to $60 for parts, while pilot assemblies or gas valves often cost $100–$500 installed. Electronic ignition conversions typically cost more due to parts and labor.
| Part | Estimated DIY Cost | Estimated Professional Replacement |
|---|---|---|
| Thermocouple | $20–$60 | $80–$180 |
| Pilot Assembly | $30–$120 | $150–$350 |
| Gas Valve | Not Recommended DIY | $300–$700 |
| Electronic Ignition Conversion | Parts Only $100–$300 | $400–$1,000+ |
Energy And Safety Considerations
Standing pilot lights consume gas continuously, typically using 600–1,500 BTU/hour depending on the pilot size. Over a heating season, that adds up and affects utility bills. Electronic ignition systems eliminate that continuous draw, improving energy efficiency and reducing emissions.
Safety is paramount. Carbon monoxide (CO) risk increases if combustion is incomplete or venting fails. Install and maintain CO detectors near sleeping areas and the furnace room, and schedule annual inspections by qualified technicians.
Upgrading From A Pilot Light To Electronic Ignition
Upgrading a furnace from a standing pilot to electronic ignition can improve efficiency and reliability. Many modern furnaces already include direct ignition systems. Conversion may be cost-effective if the furnace is otherwise in good condition and expected to remain in service for several more years.
Consider factors like furnace age, replacement part availability, conversion cost, and energy savings. A professional can assess whether an upgrade or full furnace replacement delivers the best long-term value.
Local Codes, Utilities, And Rebates
Local building codes and utility regulations affect natural gas appliance installation and repair. Some utilities and energy-efficiency programs offer rebates for upgrading to high-efficiency furnaces or electronic ignition systems. Homeowners should check with local utility companies and state energy offices for incentives.
Licensed contractors can often help identify and process available rebates, ensuring that installations meet program requirements and local codes.
Maintenance Best Practices
Regular maintenance prolongs furnace life and reduces pilot-related issues. Recommended tasks include annual inspections, cleaning the pilot orifice and burners, checking the thermocouple and gas valve, replacing air filters monthly during heavy use, and ensuring proper venting and combustion airflow.
Scheduling preventive maintenance before the heating season helps identify pilot light or ignition problems early, improving safety and comfort while avoiding costly emergency repairs.
FAQs About Gas Furnace Pilot Lights
Why Does The Pilot Keep Going Out?
Common reasons include a failing thermocouple, draft blowing out the flame, a clogged pilot orifice, low gas pressure, or a faulty gas control valve. Persistent outages warrant professional diagnosis.
Is It Safe To Relight A Pilot Light?
Relighting is safe when following manufacturer instructions, ensuring no gas smell, and confirming proper ventilation. If gas is smelled, evacuation and calling the gas company are required.
Can A Homeowner Replace A Thermocouple?
Replacing a thermocouple is a feasible DIY task for those comfortable with basic tools and following safety steps, but a professional should perform work involving gas valves or complex diagnostics.
Should A Pilot Light Be Blue?
Yes. A healthy pilot flame is blue with a small inner cone. Yellow or orange flames indicate incomplete combustion and possible CO risk, necessitating service.
Resources And Further Reading
For authoritative guidance, consult manufacturer manuals, the U.S. Consumer Product Safety Commission for gas appliance safety, the Environmental Protection Agency for efficiency information, and local utility programs for rebates. Always choose licensed HVAC professionals for gas-related repairs and installations.
For emergency situations or suspected gas leaks, contact the local gas utility or emergency services immediately. Regular maintenance and awareness of pilot light behavior improve safety and furnace performance.