How to Light a Pilot Light on a Furnace Safely and Effectively

The pilot light on a furnace is a small flame that ignites the burner when heat is needed. Knowing how to light a pilot light on a furnace is a practical skill for homeowners and renters in the U.S., reducing downtime and avoiding unnecessary service calls. This guide covers safety, step-by-step instructions, troubleshooting, and maintenance tips to keep a furnace pilot light reliable and efficient.

Item	Details
Time Required	10–30 Minutes Depending On Access And Troubleshooting
Tools Needed	Flashlight, Long Match/Lighter (If Needed), Wrench/Philips Screwdriver
Common Causes Of Failure	Dirty Or Misaligned Pilot, Faulty Thermocouple, Gas Supply Issues
When To Call A Pro	Gas Smell, Repeated Outages, Thermocouple Replacement, Complex Repairs

How A Furnace Pilot Light Works

The pilot light is a continuously burning flame that ignites the main burner when the thermostat signals for heat. Traditional standing pilot systems keep a small flame always on, while electronic ignition systems use a spark or hot surface igniter instead. This article focuses on standing pilot light furnaces where manual lighting may be required.

When To Light The Pilot Light

A furnace pilot light typically needs relighting after a power interruption, a gas shutoff, maintenance, or if drafts extinguish the flame. Before attempting to light the pilot, confirm the furnace is designed with a standing pilot and not an electronic ignition system; the owner’s manual or the furnace label can clarify this.

Safety Precautions Before Lighting

Safety First: Gas is flammable and can be dangerous when handled improperly. Always follow these precautions before attempting to light a pilot light on a furnace.

• Turn Off Power And Gas: If the furnace has an on/off switch or circuit breaker, switch off power to the unit before starting work.
• Ventilate The Area: Open windows and doors to disperse any accidental gas buildup.
• Check For Gas Odor: If a rotten egg or strong gas smell is present, do not attempt to light anything. Evacuate the home and call the gas utility or 911.
• Keep Flames Away: Avoid smoking or using open flames near the furnace until the pilot is lit and stable.

Tools And Parts To Know

Most pilot light relighting tasks require no special tools, but having the right items helps. Keep a flashlight, long fireplace match or utility lighter, adjustable wrench, and a small brush handy. Replacement parts commonly needed include a thermocouple and pilot assembly components.

Step-By-Step: How To Light A Pilot Light On A Furnace

1. Locate The Pilot Assembly

Find the furnace access panel and remove screws if necessary. The pilot assembly is near the gas control valve and will include a small burner, pilot tube, and pilot light opening. The gas control valve typically has OFF, PILOT, and ON settings.

2. Turn Gas Control To Off And Wait

Rotate the gas control knob to the OFF position and wait at least five minutes to allow any residual gas to clear. This minimizes the risk of accidental ignition from trapped gas.

3. Set Gas Control To Pilot

After waiting, set the gas control to PILOT. Press and hold the knob down to allow gas to reach the pilot. A small hole near the pilot assembly may be visible where the flame should appear.

4. Ignite The Pilot

While holding the gas control knob depressed, use a long match or utility lighter to ignite the pilot through the pilot opening. Continue holding the knob for 20–60 seconds to heat the thermocouple before releasing.

5. Confirm The Pilot Stays Lit

Release the knob; the pilot flame should remain steady and envelop the thermocouple tip. If the pilot goes out immediately, repeat steps or move to troubleshooting. If it stays lit, turn the gas control to ON and restore power to the furnace.

Troubleshooting Pilot Light Problems

When a pilot light will not stay lit or is hard to light, underlying issues often involve the thermocouple, pilot orifice, gas pressure, or drafts. Troubleshooting steps help diagnose the cause before replacing parts or calling a technician.

Thermocouple Issues

The thermocouple senses the pilot flame and signals the gas valve to stay open. If the thermocouple is dirty, bent, or worn, it may fail to detect heat and shut the gas valve, extinguishing the pilot. Inspect for soot buildup, correct alignment, and tight connection to the gas valve.

Pilot Orifice Blockage

Dirt, spider webs, and dust can clog the small pilot orifice. Clean the orifice gently with compressed air or a soft brush. Avoid using metal tools that may enlarge or damage the orifice opening.

Drafts And Venting Problems

Strong drafts or negative pressure near the pilot can blow out the flame. Check for open windows, ventilation fans, or duct issues that create airflow around the furnace. Ensure the furnace cabinet and venting are intact and properly sealed.

Gas Supply And Pressure

Low gas pressure or a closed gas valve upstream can prevent proper ignition. Confirm the main gas shutoff is open. If multiple gas appliances show low pressure, contact the gas utility or a qualified service technician.

Common Pilot Light Flame Characteristics

• Blue Flame: Healthy pilot flame with good combustion.
• Yellow Or Flickering Flame: Indicates partial combustion or contamination; clean the pilot and check venting.
• Weak Or Small Flame: Suggests low gas pressure or a blocked orifice.

Maintenance To Prevent Pilot Light Issues

Regular maintenance keeps the pilot light reliable and reduces the chance of unexpected outages. Recommended actions include annual furnace service, keeping the area clean, and checking the pilot and thermocouple for signs of wear.

• Schedule Annual HVAC Inspections: A qualified technician can clean the pilot assembly and test the thermocouple and gas valve.
• Clean Around The Furnace: Remove dust, debris, and cobwebs that can obstruct airflow or pilot orifice.
• Check Venting And Flues: Ensure proper draft and clear flues to avoid combustion and carbon monoxide issues.

When To Call A Professional

Some pilot light issues require professional service. Contact an HVAC technician or gas utility when there is a persistent gas smell, repeated pilot outages after cleaning, needed thermocouple or gas valve replacement, or unfamiliar noises and smells during operation.

Replacement Parts And Costs

Typical replacement parts include the thermocouple, pilot assembly, and gas control valve. Costs vary widely: a thermocouple part may cost $20–$75 plus labor, while a gas control valve replacement could run several hundred dollars including installation. Always obtain multiple quotes for major repairs.

Safety And Carbon Monoxide Awareness

While pilot lighting is generally safe when procedures are followed, improper combustion can produce carbon monoxide (CO). Install CO detectors near sleeping areas and follow manufacturer recommendations for venting and maintenance. If CO detector alarms, evacuate and call emergency services.

FAQ: Quick Answers

Why Won’t My Pilot Stay Lit?

Most often due to a faulty thermocouple, pilot orifice blockage, draft, or gas supply issue. Inspect and clean the assembly, then test the thermocouple and gas valve.

How Often Should The Pilot Be Relit?

A pilot light should remain lit continuously; frequent outages suggest an underlying problem that should be addressed rather than repeated relighting.

Is It Dangerous To Light A Pilot Light?

When following safety steps, lighting a pilot is safe. Do not attempt if a strong gas odor exists or if uncertain about the furnace type or condition; call a professional.

Can A Homeowner Replace A Thermocouple?

Some homeowners with basic mechanical skill can replace a thermocouple. If unfamiliar with gas systems or uncomfortable working with gas components, hire a licensed HVAC technician.

Key Takeaways And Best Practices

Know The System: Verify whether the furnace uses a standing pilot before attempting to light. Follow safety steps including gas odor checks and ventilation. Clean and inspect the pilot assembly regularly, and address recurring issues promptly to avoid safety hazards and costly repairs. For complex issues or persistent problems, consult a licensed HVAC professional.