Gas Furnace Pilot Light Guide: Troubleshooting, Relighting, and Safety

The pilot light on a gas furnace is a small flame that ignites the main burners. This guide explains how pilot lights work, common problems, safe relighting steps, and when to call a professional. It offers practical troubleshooting for homeowners and highlights modern alternatives like electronic ignition systems.

Issue	Likely Cause	Quick Action
Pilot Won’t Stay Lit	Faulty thermocouple or draft	Check thermocouple, inspect for drafts, call technician
Pilot Won’t Light	Blocked pilot or gas supply issue	Clear debris, verify gas valve, call pro if needed
Weak Flame	Clogged orifice or low gas pressure	Clean orifice, check gas line, schedule service

Relighting a pilot light can be safe if done carefully. If the furnace or gas smells strongly of gas, evacuate the area and call the gas company or emergency services. Otherwise follow the manufacturer’s instructions on the furnace data plate.

1. Turn Off Gas And Power: Set the furnace switch to “Off” and shut the gas valve for five minutes to clear any accumulated gas.
2. Locate Pilot Assembly: Find the pilot light access; consult the furnace manual for the exact location and lighting instructions.
3. Set Control To Pilot: Turn the gas control knob to the “Pilot” position and depress it while lighting the pilot with a long lighter or match.
4. Hold The Knob: Continue holding the control knob for 20–60 seconds after lighting to heat the thermocouple.
5. Release Slowly And Test: Release the knob. The pilot should remain lit. If it goes out, repeat once or twice; persistent failure requires service.

When To Stop DIY And Call A Professional

Homeowners should call a licensed HVAC technician if the pilot won’t stay lit after several relighting attempts, if the pilot flame is irregular or yellow, if gas odors are present, or if the furnace repeatedly cycles off. Issues like faulty thermocouples, gas valve defects, and control board failures require specialized tools and gas-safety expertise.

Signs To Call A Pro: persistent pilot outage, gas smell, frequent cycling, visible corrosion, or if the pilot assembly is inaccessible or damaged.

Thermocouple And Flame Sensor: Diagnosis And Replacement

The thermocouple and modern flame sensors serve similar safety roles. Testing requires a multimeter or practical replacement to confirm function. A worn thermocouple typically fails to hold the gas valve open even with a visible pilot flame.

Replacement is generally straightforward but should be performed by a qualified technician if the gas valve or control is suspect. Typical costs range depending on part and labor, with thermocouple replacement often being moderate and control board or gas valve work costing more.

Maintenance Tips To Prevent Pilot Light Problems

• Schedule Annual Furnace Tune-Up: Professional inspections catch pilot orifice buildup, thermocouple wear, and combustion issues.
• Keep Area Clean: Remove dust, debris, and nests from the furnace compartment and venting to prevent drafts and blockages.
• Check Ventilation: Ensure flues and vents are unobstructed and that exhaust paths are sealed and functional.
• Watch For Corrosion: Moisture and rust around the pilot assembly or gas line can indicate more serious problems.

Costs And Options: Repair Vs. Upgrade

Simple pilot relighting and minor repairs are inexpensive, but repeated pilot problems can justify upgrades. Replacing a thermocouple is relatively low-cost, often under a few hundred dollars installed.

Upgrading to an electronic ignition or sealed-combustion system eliminates the standing pilot and improves efficiency. Conversion costs vary by furnace model; incentives or rebates may be available that offset expense through energy savings.

Safety Precautions And Best Practices

Always follow manufacturer instructions and local codes. Never try to repair gas valves, gas lines, or controls without certification. If the area smells like gas, avoid creating sparks and leave immediately to call the gas company or emergency services.

Basic Safety Rules: ventilate only under professional guidance, keep ignition sources away during suspected leaks, and ensure carbon monoxide detectors are installed and tested regularly.

Frequently Asked Questions About Pilot Lights

How Often Should The Pilot Be Relit?

A standing pilot should rarely need relighting if the system is functioning properly. Frequent relights indicate an underlying problem that needs inspection.

Can A Homeowner Replace A Thermocouple?

Technically yes, some homeowners can replace a thermocouple following clear instructions and with the gas turned off. However the job requires caution and verifying that the replacement resolves the issue safely.

Is It Cheaper To Keep A Pilot Or Install Electronic Ignition?

Electronic ignition systems save gas and reduce maintenance but have upfront costs. Long-term savings on fuel and reduced service calls often make ignition upgrades cost-effective, especially in colder climates.

Does A Pilot Light Cause Carbon Monoxide?

A properly burning blue pilot flame does not produce dangerous carbon monoxide in normal operation. Yellow or sooty flames indicate incomplete combustion and should be addressed immediately.

Resources And Further Reading

Homeowners should consult the furnace manufacturer’s manual, the local gas utility guidance, and EPA or Department of Energy resources on furnace safety and efficiency for detailed, model-specific information.