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

Normal furnace operation with no errors present: Red LED is ON, and Green LED is OFF. If there is an error, the LED code number and/or flash sequences.

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

  • Red light is flashing quickly, and Green light is flashing slowly = Reversed polarity
    What to do: Check electrical wiring.
  • Red light is flashing slowly, and Green light is flashing quickly = Low flame error.
    What to do: Check the flame sense rod and flame sensor. Check the gas pressure.
  • Red light is flashing slowly, and Green light is solid = the High limit switch is open.
    What to do: Check the furnace filter, check the blower wheel and ductwork.
  • Red light is off, and Green light is flashing slowly = Draft inducer or pressure switch failure.
    What to do: Check the draft inducer; check the exhaust vent.
  • Red light is on, on, off and Green light is on, off, on = Circuit board failure.
    What to do: Check the control panel or wiring.
  • Red and green lights alternating, flashing slowly = Flame failure
    What to do: Check the pilot light or ignition sensor.
  • Red and green lights alternating, flashing quickly = Issue with voltage
    What to do: It could be the improper main ground.

Lennox Allert Codes

The following are the most common Lennox alert code.

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.

If you cannot read or troubleshoot the Lennox error codes, you should schedule an appointment to help determine your furnace problem.

Many furnace problems will require the help of a professional HVAC technician. In some cases, if an issue is not correctly solved, it can be more harmfull. If you aren’t a trained professional, it’s recommended that you consult an expert to address the Lennox furnace error codes.

About 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.