Lennox Furnace Error Codes: Your Essential Troubleshooting Guide

Posted by: Mas Broto
Lennox Error Codes and Troubleshooting Guides

Lennox furnaces have built-in safety features and the ability to communicate error codes. You should learn and prepare yourself for a list of expected system errors. In this guide, you’ll find out what all Lennox furnace error codes mean and what you should do to try and fix the problem.

Understanding these Lennox error codes makes furnace repairs faster and more cost-effective.

Lennox furnaces use blinking red and green LED lights to display error codes. The light will flash for the sequence, pause, and then flash again. To read the code, note its blinking pattern and count how many light flashes.

To determine what a particular light combination signifies, consult the installation guide for your particular Lennox furnace model.

These LED lights are located in the bottom compartment. Remove the front cover of the furnace, and you will find a row of LEDs.

Lennox furnace LED Lights

How to Read Lennox Furnace Error Codes

Understanding how to read the error codes on your Lennox furnace is crucial for effective troubleshooting. Lennox furnaces use a system of LED lights to indicate operational status and errors.

Let’s begin by exploring some common Lennox furnace error codes. These codes are your furnace’s way of signaling a problem, ranging from minor issues to more serious ones.

Here’s a guide to deciphering these codes:

  1. Normal Operation: If there are no errors, the Red LED will be ON, and the Green LED will be OFF. This indicates that the furnace is functioning normally.
  2. Reversed Polarity Error
    • LED Indication: Red light flashing quickly, Green light flashing slowly.
    • What to Do: Check the electrical wiring of the furnace. Reversed polarity can lead to significant electrical issues.
  3. Low Flame Error
    • LED Indication: Red light flashing slowly, Green light flashing quickly.
    • What to Do: Inspect the flame sense rod and the flame sensor. It’s also advisable to check the gas pressure to ensure it’s within the proper range.
  4. High Limit Switch Open
    • LED Indication: Red light flashing slowly, Green light solid.
    • What to Do: This usually points to airflow problems. Check the furnace filter, blower wheel, and ductwork for any obstructions or dirt accumulation.
  5. Draft Inducer or Pressure Switch Failure
    • LED Indication: Red light is off, Green light flashing slowly.
    • What to Do: Inspect the draft inducer motor and check the exhaust vent for any blockages or issues.
  6. Circuit Board Failure
    • LED Indication: Red light is on, on, off, and Green light is on, off, on.
    • What to Do: This error typically indicates a problem with the control board or internal wiring. It may require professional assessment and repair.
  7. Flame Failure
    • LED Indication: Red and green lights alternating, flashing slowly.
    • What to Do: Check the pilot light or ignition sensor. Flame failure can result from issues with gas supply or ignition components.
  8. Voltage Issue
    • LED Indication: Red and green lights alternating, flashing quickly.
    • What to Do: This could indicate an issue with the main ground or overall voltage supply to the furnace.

And here are a full list of Lennox allert codes you might attend when your furnace starts having problems.

Allert CodeTroubleshooting Tip
error code 11The thermostat cannot find a previously installed system component.
  • Check all system components (devices) connections to make sure they are Lennox communicating compatible.
  • Cycle system power.
error code 31The applicable system component is resetting itself. This issue may occur during a power outage or power fluctuation in the system.
  • Check the power connections.
  • Check the amperage draw at the transformer (possible overloaded)
error code 200The furnace roll out limit switch is open. Correct the cause of roll out trip.
  • Reset roll out switch.Test the furnace operation.Check for blocked or obstructed vent pipe (Intake and/or Exhaust).Check for flame stability, if flame is unstable, look for cause.
error code 201Lost communication with indoor blower motor.
Possible causes include power outage, brown-out, motor not powered, loose wiring, condensation on system component control without cover on breaker. Problem may be on system component control or motor side.
error code 204There is an issue with the furnace gas valve.
error code 207The furnace hot surface igniter is open.
  • Measure the resistance of hot surface igniter.
  • Replace the igniter if it is not within the specified range found in furnace installation instruction.
error code 223The furnace low pressure switch is open.
error code 224The furnace low pressure switch is stuck closed.
error code 240Could be either low flame current or a loss of flame while in run mode.

Lennox Error Code Lookup

You can also use Error Code Lookup App provided by Lennoxpros. It provides you with troubleshooting steps, instructions on how to clear the Lennox error code and determine if the situation is critical, moderate, or minor directly from a mobile device.

Lennox Error Code Lookup is available FREE to any technician who services Lennox products.


To diagnose the Lennox error codes accurately, refer to your Lennox furnace’s user manual. It usually provides a comprehensive list of error codes along with their meanings. Pay attention to the furnace’s LED light sequence, as it’s a reliable indicator of the specific issue.

While some error codes can be addressed with simple DIY fixes, others may require professional expertise, especially if they involve electrical components or gas supply. If the issue persists after your initial troubleshooting, it’s time to call a certified HVAC technician.

Preventive maintenance is key to avoiding many common error codes. Regularly changing air filters, ensuring proper ventilation, and scheduling annual inspections by a professional can go a long way in keeping your Lennox furnace running smoothly.

Understanding Lennox furnace error codes is essential for quick diagnostics and effective troubleshooting. While some issues can be resolved with simple fixes, don’t hesitate to seek professional assistance when needed. Regular maintenance can also help prevent many of these issues.

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Mas Broto

Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.

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