HVAC Fault Finder

Lennox Furnace Error Codes

Introduction

Lennox furnaces include onboard diagnostic systems that monitor the heating cycle and alert homeowners and service technicians when a problem is detected. Depending on the furnace model and control board, diagnostic information may be displayed using LED flash codes, alphanumeric codes, or a combination of both. These codes help identify operating conditions quickly and can significantly reduce troubleshooting time.

Common Lennox furnace error codes relate to ignition failures, pressure switch faults, flame sensing problems, limit switch trips, blower operation, venting restrictions, and electronic control issues. While some conditions can be resolved with basic maintenance, others require specialized tools and professional diagnosis. Because Lennox has used several different control boards across its furnace product lines, the meaning of an error code may vary by model. Always verify your furnace model before relying on a specific code description.

This page serves as the central index for Lennox furnace error codes published on HVACFaultFinder.com. Each error code links to a detailed guide explaining what the code means, common causes, safe homeowner inspections, and when professional service is recommended.

Lennox Furnace Error Code Index

Common Lennox Furnace Problems

Ignition Problems

Ignition faults occur when the burners fail to light or cannot maintain a stable flame. Common causes include igniter failures, gas supply issues, dirty flame sensors, or burner problems.

Related codes:

Pressure Switch Problems

Pressure switch faults indicate that the furnace cannot verify proper draft before ignition. Common causes include blocked vent pipes, clogged condensate drains, damaged pressure tubing, or inducer motor problems.

Related codes:

High Temperature Safety Devices

Limit switch faults protect the furnace from overheating caused by restricted airflow or abnormal operating conditions.

Related codes:

Frequently Asked Questions

Where is the diagnostic display located?

Most Lennox furnaces display diagnostic information on the integrated control board behind the blower compartment door. Many models include a viewing window so the LED can be read without removing the access panel.

Can I reset a Lennox furnace?

Some faults clear automatically after the underlying issue has been corrected. Repeatedly cycling power without identifying the root cause may result in recurring shutdowns or lockouts.

Are Lennox error codes the same on every model?

No. Lennox has produced many furnace families with different diagnostic systems. Always verify your furnace model before following troubleshooting guidance.

When should I call an HVAC technician?

Professional service is recommended whenever an error code repeatedly returns, involves gas combustion, electrical testing, safety controls, or requires replacement of furnace components.

Related Troubleshooting Guides

Safety Reminder

Many furnace error codes involve gas combustion, electrical components, or built-in safety controls. Homeowners can safely inspect items such as air filters, vent terminations, and visible wiring, but gas valves, ignition systems, pressure testing, and electrical diagnostics should be performed only by qualified HVAC professionals. If you smell gas or suspect unsafe furnace operation, leave the area immediately and contact your gas utility or emergency services from a safe location.