Light Gas Furnace Pilot: Troubleshooting, Relighting, and Safety

The pilot light on a gas furnace is a small flame that ignites the main burner; issues with the pilot cause many heating problems. This article explains how a light gas furnace pilot works, common failures, safe relighting procedures, differences between pilot and electronic ignition, troubleshooting steps, repair options, and when to call a professional.

Item	Quick Facts
Pilot Type	Standing Pilot Or Intermittent Pilot/Electronic Ignition
Common Issues	Clogged Or Drafted Pilot, Faulty Thermocouple, Gas Valve Problems
Relight Difficulty	Requires Proper Steps; If Repeated, Call Technician
Typical Cost	$50–$400 For Repairs; $300–$1,200 To Replace With Electronic Ignition

What Is A Light Gas Furnace Pilot And How It Works

A standing pilot is a continuously burning small flame that ignites the furnace’s main burners when heat is needed. It relies on a pilot assembly, a gas supply, and a thermocouple or thermopile sensor to confirm flame presence. When a thermostat calls for heat, the furnace allows gas to the main burners and the pilot lights them.

Many newer furnaces use electronic ignition systems (hot surface igniters or intermittent pilot systems) that eliminate a continuously burning pilot to save fuel and improve safety.

Common Problems With Pilot Lights

Pilot light problems include a pilot that won’t stay lit, weak flame, or a flame that keeps going out. Causes range from a dirty or misaligned pilot orifice to a failing thermocouple, drafts, or gas supply issues.

• Clogged Pilot Orifice: Dust or spider webs can reduce gas flow and weaken the flame.
• Faulty Thermocouple/Thermopile: These sensors detect flame and keep the gas valve open; when failing, they cause the valve to close.
• Gas Valve Malfunction: The valve that controls pilot gas may be defective or corroded.
• Drafts Or Venting Issues: Strong air currents or chimney/vent blockages can extinguish the pilot.
• Low Gas Pressure: Municipal or propane supply problems reduce pilot flame strength.

Is It Safe To Relight A Light Gas Furnace Pilot?

Relighting a pilot is commonly done safely by homeowners if instructions are followed and there is no smell of gas. If a strong gas odor exists or a previous gas leak was suspected, vacate the home and call the gas company or emergency services immediately.

Basic safety principles include turning off the gas and waiting recommended times for any accumulated gas to disperse, following the furnace manufacturer’s relighting steps, and ensuring adequate ventilation. Use caution and do not attempt repairs beyond basic cleaning and relighting if uncertain.

Step‑By‑Step: How To Relight A Light Gas Furnace Pilot

Before starting, find the furnace’s pilot assembly and consult the owner’s manual for model-specific directions. The general steps below apply to most standing‑pilot systems.

1. Turn Off The Gas Control: Rotate the gas valve knob to the OFF position and wait at least 5 minutes for gas to clear.
2. Set To Pilot: Move the control to the PILOT position.
3. Light The Pilot: Hold a long lighter or match near the pilot opening and press the pilot button while igniting. Hold the button for 20–60 seconds to allow the thermocouple to heat.
4. Release The Button: If the pilot remains lit, release the button slowly. If it goes out, repeat the sequence once or twice.
5. Restore Heat Mode: When the pilot stays lit, turn the control to the ON position and set the thermostat higher to call for heat.

If relighting fails after two or three attempts, stop and troubleshoot deeper causes or call a licensed HVAC technician.

Troubleshooting When The Pilot Won’t Stay Lit

If the pilot lights but does not remain lit, check the thermocouple, pilot flame shape, and possible drafts. A healthy pilot flame should be blue and surround the thermocouple tip. A yellow or weak flame indicates combustion problems.

• Thermocouple Adjustment/Replacement: Tighten the thermocouple connection to the gas valve if loose. Replace the thermocouple if cleaning and adjustment fail.
• Clean The Pilot Orifice: Use compressed air or a fine needle to clear debris; avoid enlarging the orifice.
• Shield From Drafts: Check nearby vents, doors, or attic access for drafts; relocate or block drafts temporarily during testing.
• Inspect Gas Supply: Confirm other gas appliances function. Low gas pressure requires contacting the gas utility or propane supplier.

When The Problem Is The Thermocouple Or Thermopile

The thermocouple or thermopile converts flame heat into a small electrical signal that keeps the gas valve open. Over time these sensors can fail due to corrosion or misalignment. Symptoms include pilot staying lit intermittently or going out when the pilot button is released.

Replacement is straightforward for a handy homeowner with the right part, but proper diagnosis is essential. A multimeter can check for millivolt output; a bad sensor produces low or no voltage when heated by the pilot flame.

Pilot Light Versus Electronic Ignition: Pros And Cons

Many homeowners consider converting from a standing pilot to an electronic ignition system. Both have advantages:

Feature	Standing Pilot	Electronic Ignition
Energy Use	Continuous gas consumption	No continuous pilot gas, lower operating cost
Reliability	Simple, proven technology	Fewer flame‑out issues but more electronic components
Cost	Lower upfront cost	Higher replacement cost but energy savings

Converting to electronic ignition can save fuel and reduce maintenance, but conversion cost varies by furnace model and local labor rates.

Maintenance Tips To Keep The Pilot Light Reliable

Routine maintenance reduces pilot light failures. Recommended actions include annual furnace inspections by a qualified technician, cleaning the pilot assembly, and ensuring the venting system is clear.

• Annual Tune‑Up: A technician will inspect the pilot, burners, gas valve, thermocouple, and venting.
• Keep Area Clean: Keep dust, insulation debris, and pests away from the pilot assembly.
• Check For Drafts: Seal gaps and check flue draft to reduce pilot extinguishing.
• Monitor Gas Odors: Immediately report any gas smell to the gas company and avoid operating the furnace until cleared.

Costs And When To Replace Components

Common pilot‑related repairs and approximate U.S. cost ranges are: thermocouple replacement $50–$150, pilot assembly cleaning or adjustment $50–$120, gas valve replacement $150–$600, and conversion to electronic ignition $300–$1,200 or more depending on the furnace.

Replace components when cleaning and adjustment do not stabilize the pilot or when parts are visibly corroded. Consider full ignition conversion if the furnace is older and energy savings justify the investment.

When To Call A Professional

Call a licensed HVAC technician or gas company when there is a persistent gas odor, repeated pilot outages after basic troubleshooting, suspected gas valve failure, venting or carbon monoxide concerns, or if the homeowner is uncomfortable performing relighting or part replacement.

Professionals provide safe diagnostics, millivolt testing of thermocouples/thermopiles, gas pressure checks, and proper venting and combustion analysis to prevent hazards.

Safety And Carbon Monoxide Considerations

A malfunctioning pilot or burner can cause incomplete combustion and produce carbon monoxide (CO). Homes with gas appliances should have working CO detectors on each level and follow manufacturer guidance for ventilation and service.

Signs of incomplete combustion include soot, yellow burner flames, excessive moisture on windows, or occupants experiencing headaches and nausea. If CO is suspected, leave the home immediately and call emergency services.

Frequently Asked Questions About Light Gas Furnace Pilots

Why Does The Pilot Keep Going Out After Relighting?

Common causes include a failing thermocouple, clogged orifice, drafts, or low gas pressure. If relighting fails repeatedly, stop and call a professional for diagnosis.

Can A Homeowner Replace A Thermocouple?

Yes, homeowners with basic mechanical skills can replace a thermocouple if they obtain the correct part and follow safety steps. If unsure, hire a certified HVAC technician.

Is It Worth Converting To Electronic Ignition?

Conversion can reduce fuel usage and modernize an older system. Evaluate cost versus expected fuel savings and consider furnace age and remaining service life.

How Often Should The Pilot Assembly Be Cleaned?

Inspect annually during routine maintenance; clean more often if the furnace is in a dusty environment or pests are present.

Key Takeaways

Regular maintenance, correct relighting procedures, and prompt professional help for persistent issues keep a light gas furnace pilot reliable and safe. Homeowners should prioritize safety, recognize warning signs like gas odors and soot, and install carbon monoxide detectors to protect occupants.