How to Relight a Furnace Safely and Effectively

Relighting a furnace is a common homeowner task when a pilot light goes out or an electronic ignition needs resetting. This guide explains step-by-step procedures for both pilot light furnaces and modern electronic ignition systems, prioritizing safety and compliance with manufacturer instructions. Follow all local codes and call a professional if unsure.

Furnace Type	Common Cause	Quick Action
Standing Pilot (Older Furnaces)	Pilot Out, Draft, Thermocouple Fault	Relight Pilot Per Manufacturer Steps
Electronic Ignition (Most Modern)	Ignitor Failure, Control Lockout, Gas Valve Issue	Reset System Or Replace Ignitor/Call Pro
Direct Spark	Igniter Or Control Board	Reset Power & Test Ignition Sequence

Understanding Furnace Ignition Types

Before relighting, it is essential to identify the furnace ignition type. Furnaces typically use a standing pilot, electronic hot surface ignitor, or direct spark/electronic spark system. Each type requires different procedures.

Standing pilot systems have a small continuously burning flame that lights the main burners. Electronic systems light only when heat is needed and use either a glowing ignitor or a spark to ignite gas.

Safety Precautions Before Attempting To Relight

Safety must be the priority. If the furnace area smells strongly of gas, do not attempt to relight. Evacuate the home, call the gas company or 911, and wait for clearance from professionals.

Turn off electricity to the furnace at the breaker before opening panels. Wear safety gloves and eye protection when working near gas and burners. Keep a long-reach lighter or pilot lighting tool on hand for pilot relights.

How To Relight A Standing Pilot Furnace

Step-By-Step Pilot Relight Procedure

Locate the furnace access panel and find the gas valve assembly with the pilot light instructions. The valve should have labels such as OFF, PILOT, and ON.

Turn the thermostat to the lowest setting and switch the furnace off. Close the gas valve to OFF, wait 5–10 minutes for residual gas to clear, then switch valve to PILOT.

Press and hold the gas valve’s pilot button while applying a long-reach lighter to the pilot opening or using the furnace’s built-in igniter. Maintain pressure for 30–60 seconds after the pilot establishes to warm the thermocouple.

Release the pilot button slowly. If the pilot stays lit, turn the valve to ON, replace access panels, restore power, and set thermostat to desired temperature. If the pilot will not stay lit, try cleaning the pilot or proceed to troubleshooting steps.

Common Issues With Standing Pilot Systems

• Thermocouple Failure: If the pilot lights but goes out when the pilot button is released, the thermocouple may be weak or misaligned and likely needs replacement.
• Pilot Orifice Clogging: Debris or soot can block the pilot orifice. Cleaning with compressed air or a fine needle can restore flow.
• Drafts: Strong drafts from open windows or holes in ductwork can extinguish the pilot. Address airflow issues and ensure the furnace enclosure is sealed.

How To Reset And Relight Electronic Ignition Furnaces

Most modern furnaces use an electronic hot surface ignitor or a direct spark system. These do not have a standing pilot to relight. Instead, relighting involves resetting or addressing hardware faults.

Basic Reset Steps

Locate the furnace power switch or breaker and turn the unit off for 30 seconds, then restore power. Many control boards will reset fault codes and allow a new ignition cycle.

Set the thermostat to call for heat and observe the ignition sequence through the furnace access panel window or view ports. The sequence usually includes a blower pre-purge, gas valve energize, and ignitor glow or spark. If the ignitor glows but no flame appears, the issue may be the gas valve or gas supply.

Troubleshooting Electronic Ignition Problems

• Ignitor Failure: Hot surface ignitors are fragile and often visible as a ceramic element. Cracks or absent glow indicate replacement is needed.
• Control Board Lockout: Repeated ignition failures can cause lockout. Resetting power may clear it, but persistent failures require diagnosing the root cause such as flame sensor or gas valve.
• Flame Sensor Issues: A dirty flame sensor can prevent recognition of flame and shut off gas. Cleaning the sensor with emery cloth often restores function.

When To Call A Professional Technician

If relighting attempts fail, unusual odors persist, burners do not ignite, or the furnace cycles repeatedly into lockout, contact a licensed HVAC technician. Gas systems and electrical components pose safety risks and require professional diagnosis.

Call a professional if the ignitor is cracked, the gas valve hums but no flame appears, or if carbon monoxide detectors have triggered. Also seek service for persistent pilot outages or suspected gas leaks.

Carbon Monoxide Risks And Detection

Furnaces burning natural gas or propane can produce carbon monoxide (CO) if combustion is incomplete. CO is odorless and dangerous. Install CO detectors near sleeping areas and the furnace room.

Regular furnace inspections by certified technicians reduce CO risk. If CO alarm sounds, leave the home immediately and call emergency services or the gas company.

Maintenance Tips To Prevent Future Relighting Problems

Regular maintenance reduces ignition problems. Change filters every 1–3 months to improve airflow and reduce stress on the system. Ensure vents and flues are clear of obstructions.

Schedule annual professional tune-ups that include inspection of the pilot, ignitor, flame sensor, burners, and heat exchanger. A yearly cleaning and safety check helps detect issues early and maintain efficiency.

Checklist: Tools And Items Needed For Relighting

• Long-reach lighter or pilot lighting tool for standing pilot relights
• Flashlight to inspect burner assembly
• Screwdrivers or nut drivers to open access panels
• Protective gloves and safety glasses
• Soft emery cloth for cleaning flame sensors
• Replacement thermocouple or ignitor if diagnosed as faulty

Common Manufacturer-Specific Notes

Always follow the furnace manufacturer’s instructions found on the unit. Some manufacturers require a specific reset sequence or include safety interlocks that differ between models.

Warranty may be voided by improper DIY repairs. For newer furnaces under warranty, contact the dealer or manufacturer-authorized technician for relighting and service.

Cost Considerations For Repairs And Parts

Minor parts like thermocouples or flame sensors are relatively inexpensive, typically under $100 for parts plus labor. Hot surface ignitors and control boards can be several hundred dollars including parts and labor.

Routine maintenance costs vary by region but investing in annual service can prevent more costly failures. Always obtain multiple estimates for major repairs and verify technician licensing.

How To Document And Report Issues

Keep records of relight attempts, error codes on the furnace control board, and any unusual noises or odors. Photos of damaged components such as cracked ignitors help technicians diagnose remotely.

Documenting service dates and parts replaced supports warranty claims and helps technicians track recurring problems.

Final Practical Tips

• Never skip the gas odor check: a faint smell warrants immediate caution.
• When in doubt, shut off the gas and power and call a professional.
• Keep CO detectors on every level of the home and test them monthly.
• Consider upgrading to an electronic ignition system for improved efficiency if the existing standing pilot system is old.

Key Takeaway: Relighting a furnace depends on the ignition type. Standing pilots can often be relit with care following the correct steps, while electronic systems typically require resets or component replacement. Prioritize safety and call a licensed HVAC professional when uncertainty or persistent problems exist.