How To Relight Pilot Light Furnace: A Step-by-Step Safety Guide
Relighting a furnace pilot light requires locating the gas control valve, turning it to the pilot position, applying an external flame while depressing the safety reset button, and holding it down for 30 to 60 seconds until the thermocouple generates enough millivoltage to keep the gas valve open. Always sniff for natural gas leaks before attempting ignition, and immediately call a certified HVAC technician if you smell gas or if the pilot flame refuses to stay lit.
Pre-Operation & Equipment Checklist
Before interacting with your heating system, understanding the mechanical setup and gathering the right tools ensures a safe and efficient relighting process. Most modern high-efficiency furnaces use electronic hot surface igniters and do not have standing pilot lights; this guide applies specifically to older standing pilot furnaces equipped with a standing flame and a traditional gas control valve.
- Essential gear, tools, and materials: A long-reach utility lighter or long fireplace matches, a flashlight or headlamp, a flathead screwdriver (if access panels require removal), and a clean rag or soft brush for clearing debris around the burner assembly.
- Mandatory prerequisite knowledge and safety standards: Familiarity with the odor of mercaptan (the sulfur-like additive that makes natural gas smell like rotten eggs), knowledge of your local utility emergency shut-off procedures, and strict adherence to the manufacturer's instruction label located on the furnace chassis.
- Estimated budget and duration benchmarks: Zero cost if performed independently using household items; duration is approximately 10 to 15 minutes of active, careful operation.
Step-by-Step Pilot Light Restoration Process
Step 1: Safety Assessment and Gas Valve Location
Begin by removing the lower front access panel of your furnace to expose the burner compartment, gas control valve, and pilot assembly. Inspect the area carefully for any signs of soot, corrosion, or debris. Most importantly, pause and sniff closely around the base of the furnace for the distinct sulfur odor of a gas leak.
Warning: If you detect the smell of natural gas, stop immediately. Do not attempt to light the pilot, do not flip any electrical switches, and evacuate the building immediately. Call your local gas utility or emergency services from a safe location.
Step 2: Shut Down the Gas Supply
Locate the primary gas control knob on the valve body, which typically features three main settings: ON, OFF, and PILOT. Press down gently on the knob and rotate it from its current position (which may be ON or stuck midway due to a failed flame) to the OFF position.
Pro-Tip: Once the knob is turned to the OFF position, leave it alone for a minimum of five full minutes. This mandatory dwell time allows any residual, unburned gas inside the combustion chamber to completely dissipate into the chimney flue or room air.
Step 3: Position the Control Valve to Pilot
After the mandatory safety wait period has elapsed, press the gas control knob down and rotate it counterclockwise from OFF to the designated PILOT position. Do not release the downward pressure on the knob just yet, as internal mechanical safety gates remain engaged until the thermocouple is heated.
Step 4: Ignite the Pilot Assembly
While continuing to hold the gas control knob firmly down in the PILOT position, use your other hand to introduce a live flame directly to the pilot head. Insert a long utility lighter or a long-reach match through the designated access port until the flame sits squarely against the pilot burner opening. You should hear a soft whoosh or see a small blue flame ignite immediately.
Step 5: Maintain Pressure on the Safety Reset Button
Keep holding the gas control knob (or separate red/black reset button depending on your valve model) fully depressed for 30 to 60 seconds after the pilot flame is visible. This duration allows the flame to heat the tip of the thermocouple, generating a tiny electrical current—typically between 15 to 30 millivolts—that energizes the safety electromagnet inside the gas valve to hold the gas supply open independently.
Step 6: Release and Verify Flame Stability
Slowly and carefully release the pressure on the control knob. If the pilot flame remains lit and stable, you have successfully energized the thermocouple circuit. If the flame immediately snuffs out the moment you let go, the thermocouple has failed to generate sufficient millivoltage, requiring you to repeat the ignition sequence from Step 2.
Step 7: Rotate to the On Position and Reassemble
Once the pilot flame burns steadily on its own, push the gas control knob down slightly and rotate it fully into the ON position. You should hear a distinct click or feel the internal spring catch. Turn your household thermostat up a few degrees above the current room temperature to signal the main burners to ignite, verify that the main burner flames burn a crisp, steady blue, and securely replace the furnace access panel.
How To Relight A Pilot Light On Propane Furnace | Shelly Lighting
Furnace Ignition Systems & Troubleshooting Parameters
| Ignition System Type | Primary Identification Feature | Common Failure Modes | Standard Repair Method |
|---|---|---|---|
| Standing Pilot | Continuous small blue flame; mechanical gas valve with Pilot setting | Weak thermocouple, dirty pilot orifice, draft interference | Clean pilot tube, replace thermocouple, check venting |
| Intermittent Pilot | Spark igniter lights pilot only on demand; electronic control board | Carbon buildup on spark rod, faulty ignition control module | Clean flame sensor/igniter, test circuit board voltage |
| Hot Surface Ignition | Silicon nitride or carbide igniter glows bright orange; no pilot | Cracked igniter element, blocked pressure switch | Replace HSI element, clear condensate trap or vent lines |
Common Site Failures & Field Fixes
- Root Cause: The pilot flame goes out immediately after releasing the control knob.
- Actionable Fix: The thermocouple is either misaligned, coated in soot, or failing electrically. Clean the metal tip with fine emery cloth or a dollar bill, ensure the flame envelops the upper third of the thermocouple, or replace the thermocouple assembly using an open-end wrench.
- Root Cause: Gas does not flow to the pilot burner when the valve is in the Pilot position.
- Actionable Fix: The gas control valve is locked out, or the manual gas shut-off valve on the supply pipe is closed. Verify the supply line handle is parallel to the pipe and ensure you are depressing the control knob completely straight down before turning.
- Root Cause: The pilot flame is yellow, wavering, or lifting off the burner head.
- Actionable Fix: Improper air-to-gas mixture caused by dust or spider webs inside the pilot burner tube. Turn off the gas, allow the assembly to cool, and gently clean the pilot orifice using a specialized wire brush or compressed air.
- Root Cause: The pilot stays lit, but the main burners fail to ignite when the thermostat calls for heat.
- Actionable Fix: The gas control valve is stuck in the pilot position, the thermostat wires are loose, or the millivolt output from the thermocouple is too low to open the main gas valve. Turn the knob firmly to ON and check terminal connections.
Frequently Asked Questions
Why does my furnace pilot light keep going out?
A pilot light typically goes out due to a draft blowing the flame away, a dirty pilot orifice restricting gas flow, or a faulty thermocouple that fails to signal the gas valve to stay open. Over time, soot and carbon buildup insulate the thermocouple, preventing it from detecting the heat of the flame properly.
How do I know if my thermocouple is broken?
You can test a thermocouple using a digital multimeter set to the millivolt (mV) scale while the pilot light is burning. If the thermocouple produces less than 12 millivolts under heat, or drops below 5 millivolts when the gas valve opens, the component is defective and must be replaced.
Is it safe to relight a furnace pilot light myself?
Yes, homeowners can safely relight a standing pilot furnace by strictly following manufacturer instructions and safety dwell times. However, if you notice structural rust on the heat exchanger, hear persistent clicking without ignition, or smell persistent gas leaks, you must stop and contact a professional.
How long should I hold the pilot button down?
You must hold the pilot button down for 30 to 60 seconds after ignition. This window provides enough thermal energy for the thermocouple tip to reach operating temperature and generate the millivolts required to hold the safety valve open.
What should I do if I smell gas while trying to relight the furnace?
Immediately stop all operations, leave the gas control valve in the OFF position, and evacuate the building immediately. Do not turn on lights, use cell phones, or operate appliances inside the structure until the gas utility company or an HVAC professional clears the area.
Schedule Professional Furnace Maintenance Today
Ensure your heating system operates safely and efficiently through the coldest months by scheduling a comprehensive annual inspection with a certified HVAC technician. Protect your home and maximize equipment lifespan by booking your professional tune-up today.
