Relight Pilot Light on Furnace: A Practical Guide – Accelerate Net Zero

Relighting a furnace pilot light is a common home maintenance task, especially for older gas furnaces that use a standing pilot. When the pilot goes out, heating can be interrupted and fuel may continue to vent. This guide explains how to safely relight standing pilots, how to handle furnaces with intermittent pilots or electronic ignition, and when to call a professional. It emphasizes safety, identifies typical flame issues, and provides clear, step-by-step instructions you can follow with confidence.

Understanding Furnace Pilot Light Systems

Most U.S. homes rely on one of three pilot systems: standing pilot lights, intermittent pilot lights, and electronic ignition. Standing pilots burn a small flame continuously, so relighting is needed if the flame goes out. Intermittent pilots light only on demand via a spark or hot surface igniter and then shut off. Electronic ignition replaces a standing flame with an automatic ignition sequence controlled by the furnace’s control board. Knowing your system determines the relighting approach and safety precautions.

Standing Pilot Light

In a standing pilot system, a small flame burns at the pilot assembly at all times. If this flame goes out, relighting requires lighting the pilot and warming the thermocouple so the gas valve remains open.

Intermittent Pilot And Electronic Ignition

Intermittent pilot systems rely on a spark or hot surface igniter to light the burner only when heat is needed. Electronic ignition uses a control board to start burners without a persistent pilot flame. For these systems, relighting steps differ and often do not involve a traditional torch-style lighting of a pilot.

Safety First: Key Precautions Before Relighting

• Turn off the thermostat to prevent the furnace from attempting to ignite while you work.
• Set the gas valve to OFF if your model has a labeled Off position and wait a full five minutes to clear any accumulated gas.
• Ventilate the area by opening a door or window if you can do so safely.
• If you smell gas (rotten egg odor) or hear a hiss, leave the area immediately and contact your gas utility or emergency services.
• Keep ignition sources away from the furnace area while working.
• Use a CO detector and ensure it’s functioning in the home. If the detector alarms, evacuate and seek help.
• If you’re unsure about any step, call a licensed HVAC technician for safety and proper service.

Relighting A Standing Pilot Light

Relighting a standing pilot requires a careful sequence to light the pilot and heat the thermocouple so the gas valve stays open. The exact procedure can vary by furnace model, so consult the owner’s manual if available. The steps below reflect common configurations and are intended as a general guide for safety.

What You’ll Need

• Flashlight if visibility is low
• Long-reach, non-sparking lighter or wooden kitchen match
• Flathead screwdriver or adjustment tool if your model requires panel removal
• Safety glasses and gloves for protection

Step-By-Step Procedure

1. Turn the thermostat to Off and locate the furnace access panel. Remove the panel if needed to access the burner and pilot assembly.
2. Turn the gas control knob to the Off position and wait at least five minutes to clear gas from the line.
3. Locate the Pilot knob on the gas control valve. Move it to the Pilot position.
4. Press and hold the gas control knob firmly. While continuing to hold, use a long lighter or match to ignite the pilot flame at the pilot assembly.
5. Keep holding the knob for about 60 seconds after the pilot lights to heat the thermocouple. If the flame goes out, repeat from step 3.
6. Release the knob slowly and turn it to the On position, ensuring the main burner lights when the thermostat calls for heat.
7. Replace the access panel and restore power. If the flame remains steady, replace any covers and return the thermostat to its previous setting.

After relighting, observe the flame on the main burner. It should be a steady blue flame with little to no orange or yellow tint. Persistent yellow sooting or an extinguished flame indicates an imbalance or dirty orifice, and may require professional service.

Relighting Intermittent Pilot Or Electronic Ignition Furnaces

Furnaces that use intermittent pilots or electronic ignition do not rely on a continuously burning pilot flame. Relighting involves different practices, often centered on resetting the control board, powering cycles, or following model-specific procedures. When in doubt, consult the user manual or contact a licensed technician. The following guide provides safe, general steps.

Intermittent Pilot

With an intermittent pilot, ignition occurs on demand. If the burner fails to light after ignition attempts, ensure the gas valve is open, and reset the control system according to the manual. Avoid cranking repeatedly; prolonged attempts can overheat components and waste fuel. If lighting remains unsuccessful, a service visit is advised.

Electronic Ignition

Electronic ignition systems replace a standing flame with an automatic sequence controlled by the furnace’s control board. Common steps include turning the power switch off and on, or pressing a reset button, then returning the thermostat to heat. If the igniter glows but the burners do not ignite, this indicates an igniter, flame sensor, or gas valve issue that typically requires professional inspection.

If the ignition sequence fails after several attempts, do not force the system. Shut down power and gas, wait, and call a technician to diagnose ignition, sensor, or valve faults.

Troubleshooting Common Issues

• Pilot light won’t stay lit: Thermocouple may be dirty, misadjusted, or the gas valve isn’t receiving heat from the thermocouple. Clean or replace the thermocouple if accessible, or have a pro inspect the valve
• Burner won’t ignite after a flame: Igniter may be faulty, flame sensor needs cleaning, or gas supply is insufficient. Check gas supply valve and replace faulty components as needed
• Gas smell: Evacuate immediately and contact the gas company. Do not operate electrical switches or lights
• Frequent cycling: Could indicate a dirty air filter, restricted venting, or thermostat issues. Replace filters and ensure proper vent clearance
• CO detector alarm: Leave the area, call emergency services, and have the furnace inspected for CO leaks

Maintenance And Prevention

Regular maintenance helps prevent pilot relighting issues and extends furnace life. Schedule annual professional inspections, and perform routine checks between visits. The following practices support safe, reliable operation.

• Replace air filters every 1–3 months during heating season to maintain airflow
• Keep furnace area clear of dust, debris, and flammable materials
• Inspect venting, condensate drains, and flue pipes for blockages or damage
• Test CO detectors and replace batteries as needed
• Inspect gas lines for leaks (soapy water bubble test can help) only if you’re skilled; otherwise call a pro
• Document furnace model and maintenance history for quick reference

Ignition Type Quick Reference