How To Reset A Furnace Pilot Light: Step-by-Step Safety & Ignition Guide

Resetting a furnace pilot light requires turning the gas control valve to OFF, waiting a mandatory five minutes to allow any residual combustible gas to dissipate, and switching the valve to PILOT. While depressing the pilot reset button to override the safety shutoff valve, apply an external flame source directly to the pilot burner assembly until a steady blue flame ignites. You must hold the reset button for 30 to 60 seconds to heat the thermocouple sufficiently to generate 12 to 30 millivolts, which keeps the safety valve open after the button is released.

Pre-Relighting Safety Protocols and Equipment Setup

Safely relighting a standing pilot ignition system on a gas-fired furnace demands strict adherence to fuel gas standards, specifically National Fuel Gas Code guidelines (NFPA 54). Before attempting any physical manual ignition, you must understand the distinction between a traditional standing pilot system—which maintains a continuous flame to ignite the main burners—and modern electronic ignition systems, such as Hot Surface Igniters (HSI) or Direct Spark Igniters (DSI). Electronic ignition systems do not feature a standing pilot light and require an electrical reset via the primary breaker or thermostat rather than manual lighting.

Improper handling of natural gas (methane) or liquefied petroleum gas (propane) presents serious combustion, asphyxiation, and explosion hazards. Propane is heavier than air and settles near floor level, whereas natural gas rises. A thorough perimeter inspection using olfactory senses is required before initiating any open flame near the unit. If you detect a strong smell of sulfur or rotten eggs throughout the furnace room, do not attempt to light the pilot; immediately evacuate the premises and contact your local gas utility provider or emergency services.

Essential Gear and Tool Checklist

• Primary Ignition Source: Flexible neck butane utility lighter, long fireplace matches, or a specialized furnace match extension holder.
• Inspection Tools: High-lumen LED flashlight or headlamp to view the recessed pilot envelope and combustion chamber assembly.
• Cleaning Equipment: Brass wire tube brush, canned compressed air, or an electrical contact cleaner spray for clearing oxidation from the burner head.
• Diagnostic Tools (Optional): Digital multimeter with alligator leads to measure thermocouple DC millivoltage output.

Technical & Financial Benchmarks

• Mandatory Prerequisite Standard: NFPA 54 / ANSI Z223.1 Fuel Gas Code compliance.
• Estimated Time Required: 15 to 25 minutes (including the compulsory gas dissipation dwell period).
• Estimated DIY Cost: $0 to $15 (assuming basic lighting tools are already available).

Step-by-Step Gas Furnace Pilot Relighting Process

Step 1: Locate the Access Panel and Identify Ignition Type

Remove the outer access door on the front lower cabinet of your furnace. Most units utilize slip-fit panels that lift upward and pull outward, while older models may use thumb screws or hex-head fasteners. Once the access door is off, inspect the interior burner housing to confirm your furnace type. A standing pilot unit features a small gas tube running alongside a thin metal rod (the thermocouple) pointing toward a small burner nozzle situated near the main burner manifold.

Warning: If your furnace panel features a control board with LED diagnostic lights, a clear glass viewing port, and a thick silicone-insulated igniter wire instead of a metal gas pilot tube, you own an electronic ignition furnace. Do not attempt to light this system with a match or lighter.

Step 2: Switch the Gas Control Valve to OFF

Locate the combination gas control valve body. This metallic valve block connects the main incoming black iron gas line to the interior burners. On the top or face of this control block, identify the rotary gas valve knob, which typically features three marked positions: ON, OFF, and PILOT. Firmly turn the knob clockwise until the pointer aligns directly with the OFF position.

Step 3: Execute the Mandatory 5-Minute Gas Dissipation Wait

Once the valve knob is positioned to OFF, step away from the unit and wait at least five full minutes. This waiting period allows any accumulated natural gas or propane that backed up inside the combustion chamber to diffuse safely into the ambient room air.

Warning: Skipping the five-minute gas clearance period creates a high-risk condition where trapped residual gas can flash violently upon match introduction, leading to physical injury or equipment explosion.

Step 4: Rotate Control Valve to the PILOT Position

After five minutes have elapsed without any residual gas odor, push down slightly on the gas control knob and rotate it counterclockwise until the pointer aligns with the PILOT position. In this position, the internal spring-loaded valve blocks gas flow to the primary burner manifold while allowing manual mechanical flow exclusively to the small pilot orifice tube when the knob or button is physically depressed.

Step 5: Depress the Reset Valve and Apply Flame

Prepare your long-necked butane lighter or match. Depress the gas control knob (or a separate red reset button located adjacent to the valve, depending on the valve manufacturer model such as Honeywell or White-Rodgers) completely downward. This mechanical action manually forces open the pilot safety valve internal plunger. Simultaneously bring your flame source within one-quarter inch of the pilot burner nozzle tip located inside the combustion chamber access area.

Pro-Tip: If your lighter cannot reach the pilot assembly without your hand entering the narrow combustion enclosure, attach a match to a wire match-extension wand to keep your hands at a safe operating distance from the draft opening.

Step 6: Maintain Pressure to Heat the Thermocouple

Once the pilot flame catches and burns steady, do not immediately release the control knob or reset button. You must continue depressing the knob firmly for 30 to 60 seconds. During this holding period, the sustained pilot flame engulfs the top one-third of the thermocouple tip. The temperature differential across the bi-metal junction inside the thermocouple creates a small DC electric current via the Seebeck effect, rising from 0 millivolts up to a stable operating range of 18 to 30 millivolts.

Step 7: Release Valve and Engage Main Control to ON

After holding the reset button for at least 45 seconds, release it slowly. The pilot flame should remain continuously lit. If the flame immediately extinguishes, wait another five minutes and repeat Steps 4 through 6, holding the button down for a full 60 seconds. Once the pilot remains lit independently, push the control knob down slightly and rotate it counterclockwise to the ON position. Replace the front furnace access door securely to engage the safety door switch, then set your living space thermostat above current ambient room temperature to initiate a main burner heating cycle.

Furnace Ignition System Specifications

Understanding the operational specifications of different ignition systems helps determine maintenance schedules and evaluate component failures during the relighting process.

Pilot Light Failure Scenarios & Field Remedies

Scenario 1: Flame Extinguishes Immediately Upon Releasing the Reset Button

• Root Cause: A degraded, oxidized, or misaligned thermocouple that fails to generate the minimum open-circuit millivoltage requirement (typically 18–30 mV DC) to energize the internal magnetic holding coil of the gas control valve.
• Actionable Fix: Turn the gas valve OFF. Using a fine-grit emery cloth, light wire brush, or steel wool, gently scrub carbon deposits off the outer surface of the thermocouple copper probe. Ensure the thermocouple tip is positioned so the pilot flame directly engulfs its upper 3/8 to 1/2 inch. If the flame continues to drop out after a 60-second hold, test the thermocouple output with a multimeter set to DC millivolts. Replace the thermocouple if reading is below 12 mV DC under load.

Scenario 2: Lazy, Yellow, or Waving Pilot Flame

• Root Cause: Airway blockage inside the pilot orifice tube caused by dust, lint, spider webs, or heavy soot accumulation, resulting in an improper fuel-to-air mixture ratio.
• Actionable Fix: Shut off the gas supply line valve completely. Allow the assembly to cool down for 10 minutes. Unthread the pilot line fitting from the gas valve using a 7/16-inch open-end wrench. Carefully remove the tiny brass pilot orifice stored inside the fitting. Clear the micro-jet opening using compressed air or a soft monofilament line. Never clean the orifice hole with a drill bit or steel needle, as expanding the precise orifice diameter alters gas delivery pressure.

Scenario 3: Draft Gusts Repeatedly Blow Out the Pilot Flame

• Root Cause: Negative air pressure conditions within the utility room, a compromised flue pipe draft setup, or a missing/damaged combustion chamber door seal panel.
• Actionable Fix: Inspect the vent stack connector pipe running from the top of the furnace to the chimney or wall termination for loose joints, corrosion, or draft hood blockages. Ensure the lower furnace access panel is properly fitted with a tight seal, and check that fresh air intake grills or mechanical room louvers are unobstructed to maintain balanced atmospheric room pressure.

Scenario 4: The Gas Control Knob Will Not Depress in PILOT Position

• Root Cause: Interlock mechanical safety pin engagement caused by attempting to push the knob down while turned between defined detents, or an internal mechanical failure of the gas valve spring mechanism.
• Actionable Fix: Ensure the rotary knob alignment arrow points precisely at the marked center of the PILOT text detent. If it is slightly off-center, the internal keyway will physically block downward travel. Never apply excessive force with pliers or striking tools to a gas valve knob; if the valve body internal safety mechanism seizes permanently, replace the entire combination gas valve assembly.

Frequently Asked Questions

How long should I wait if I smell gas before attempting to relight the pilot?

If you detect a faint gas smell right near the unit, turn the gas valve to OFF and wait at least 5 to 10 minutes for the ambient air to clear. If you smell a pervasive, strong odor of gas throughout the room or basement, evacuate the home immediately without operating any electrical switches and dial 911 or your local gas utility company.

Why does my furnace pilot light keep going out repeatedly?

The most common cause of a recurring pilot light outage is a failing thermocouple that can no longer maintain the millivolt threshold needed to keep the gas valve open. Additional causes include a clogged pilot orifice, a damaged or improperly vented flue chimney that produces downdrafts, or a faulty thermal high-limit switch wired in series with the pilot circuit.

Can I relight a furnace that uses an electronic ignition system?

No, modern furnaces equipped with Hot Surface Ignition (HSI) or Direct Spark Ignition (DSI) do not feature a standing pilot light to ignite manually. If an electronic ignition furnace fails to light, reset the system by switching off the furnace electrical breaker for 30 seconds, ensuring the gas supply valve is open, and turning the breaker back on to initiate an automated purge and ignition sequence.

How much millivoltage should a healthy furnace thermocouple generate?

A healthy standing pilot thermocouple generates an open-circuit reading between 25 and 30 millivolts (mV DC) when tested outside the circuit with a multimeter. Under normal operating load while connected to the safety valve magnet, a functional thermocouple must continuously output between 12 and 15 mV DC to keep the pilot valve coil reliably energized.

Is it safe to turn off my furnace pilot light during the summer months?

Yes, turning off your standing pilot light during the warm summer months is safe and helps conserve natural gas or propane while preventing unnecessary heat accumulation around the heat exchanger. Simply turn the gas control knob to the OFF position for the season, and follow standard manual relighting steps when heating is needed again in the fall.

Professional HVAC Diagnostic & Repair Services

When manual relighting procedures fail to restore reliable furnace operation, or if your system experiences repeated lockouts, underlying component failures require expert technical intervention. Certified HVAC specialists possess specialized pressure gauges, digital manometers, and combustion analyzers necessary to diagnose hidden gas pressure dropouts or cracked heat exchangers safely. Protect your home comfort and indoor safety by scheduling a comprehensive furnace safety inspection with a licensed heating contractor today.