Lennox
Lennox Smart Thermostats Error Codes
Complete list of fault codes and troubleshooting guides. Use the search below to find your specific error.
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E200
Thermostat displays E200 and cannot communicate with the indoor unit or outdoor unit; system may not heat or cool.
Equipment Communication Fault
E201
Thermostat shows E201 and reports loss of communication with the indoor unit only; cooling or heating may not respond.
Indoor Unit Communication Loss
E202
Thermostat displays E202 indicating loss of communication with the outdoor unit; cooling or heat pump operation may be disabled.
Outdoor Unit Communication Loss
E203
Thermostat shows E203 and indicates communication error with one or more zoning dampers or zone control module.
Zoning Communication Fault
E210
Thermostat displays E210 indicating no 24V power detected on the R/C terminals; screen may be dim or rebooting.
Thermostat Power Loss
E211
Thermostat intermittently reboots or shows E211 low power warning, especially when equipment starts.
Low Voltage Drop Under Load
E220
Thermostat shows E220 indicating internal temperature sensor fault; room temperature reading is missing or obviously wrong.
Internal Thermostat Temperature Sensor Failure
E221
Thermostat displays E221 and cannot read the remote indoor temperature sensor (if installed).
Remote Indoor Sensor Fault
E222
Thermostat shows E222 indicating remote outdoor temperature sensor fault; outdoor temperature reading is missing or incorrect.
Outdoor Temperature Sensor Failure
E230
Thermostat displays E230 indicating humidity sensor fault; indoor humidity reading is unavailable or clearly wrong.
Internal Humidity Sensor Failure
E231
Thermostat shows E231 indicating remote humidity sensor fault (if a separate sensor is installed).
Remote Humidity Sensor Failure
E240
Thermostat displays E240 indicating Wi‑Fi connection failure; remote app control and cloud services are unavailable.
Wi‑Fi Connectivity Fault
E241
Thermostat shows E241 indicating loss of connection to Lennox cloud services; local control works but app access fails.
Cloud Service Communication Fault
E250
Thermostat displays E250 indicating configuration or equipment mismatch; system may not operate correctly.
System Configuration Error
E260
Thermostat shows E260 indicating internal memory or firmware error; may reboot repeatedly or lose settings.
Thermostat Firmware/Memory Fault
E270
Thermostat displays E270 indicating internal display or touch interface fault; screen may be blank, frozen, or unresponsive.
Display/Touchscreen Failure
E280
Thermostat shows E280 indicating internal fan control or G output fault; fan may not run when commanded.
Thermostat Fan Output Failure
E290
Thermostat displays E290 indicating dehumidification control fault; dehumidify function does not operate correctly.
Dehumidification Control Error
Symptom
Thermostat backlight flickers or display brightness changes unexpectedly.
Display Power Instability
Symptom
Thermostat calls for cooling but the air conditioner or heat pump does not start; fan may or may not run.
No Cooling Call Output
Symptom
Thermostat calls for heat but the furnace or heat pump does not start; no error code shown on thermostat.
No Heating Call Output
Symptom
Thermostat display is on but does not respond to touch or button presses.
Unresponsive Touchscreen
Symptom
Thermostat does not energize the fan in 'Fan On' mode, but fan runs during heating or cooling.
Fan-Only Control Failure
Symptom
Thermostat does not follow programmed schedule; temperature changes occur at wrong times or not at all.
Scheduling/Programming Fault
Symptom
Thermostat emits a burning smell or becomes unusually hot to the touch.
Overheating Thermostat Electronics
Symptom
Thermostat fails to control whole-home dehumidifier connected as a separate unit to Lennox system.
Standalone Dehumidifier Control Failure
Symptom
Thermostat fails to control whole-home humidifier connected to Lennox furnace/air handler.
Humidifier Control Failure
Symptom
Thermostat fails to control zoning properly; some zones do not heat/cool as commanded.
Zoning Control Misoperation
Symptom
Thermostat frequently disconnects from Wi‑Fi or Lennox app loses connection intermittently.
Intermittent Wi‑Fi Connectivity
Symptom
Thermostat is completely blank with no display and no response to touch or buttons.
No Power to Thermostat
Symptom
Thermostat loses date/time and custom settings after every power outage.
Loss of Non-Volatile Memory or Backup Power
Symptom
Thermostat reboots randomly several times a day without user input.
Intermittent Power or Firmware Reset
Symptom
Thermostat shows 'Equipment not responding' or similar message without a specific numeric code.
General Equipment Non-Response
Symptom
Thermostat shows 'Outdoor unit offline' but cooling still works intermittently.
Intermittent Outdoor Unit Communication
Symptom
Thermostat shows frequent 'Filter' or 'Service' reminders even after being reset.
Maintenance Reminder Configuration Issue
Symptom
Thermostat shows humidity reading that is clearly inaccurate compared to a known-good hygrometer.
Humidity Sensing Error
Symptom
Thermostat shows temperature that is clearly inaccurate compared to other thermometers in the home.
Temperature Sensing/Calibration Error
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E200 |
Thermostat displays E200 and cannot communicate with the indoor unit or outdoor unit; system may not heat or cool.
|
Equipment Communication Fault | View Details |
| E201 |
Thermostat shows E201 and reports loss of communication with the indoor unit only; cooling or heating may not respond.
|
Indoor Unit Communication Loss | View Details |
| E202 |
Thermostat displays E202 indicating loss of communication with the outdoor unit; cooling or heat pump operation may be disabled.
|
Outdoor Unit Communication Loss | View Details |
| E203 |
Thermostat shows E203 and indicates communication error with one or more zoning dampers or zone control module.
|
Zoning Communication Fault | View Details |
| E210 |
Thermostat displays E210 indicating no 24V power detected on the R/C terminals; screen may be dim or rebooting.
|
Thermostat Power Loss | View Details |
| E211 |
Thermostat intermittently reboots or shows E211 low power warning, especially when equipment starts.
|
Low Voltage Drop Under Load | View Details |
| E220 |
Thermostat shows E220 indicating internal temperature sensor fault; room temperature reading is missing or obviously wrong.
|
Internal Thermostat Temperature Sensor Failure | View Details |
| E221 |
Thermostat displays E221 and cannot read the remote indoor temperature sensor (if installed).
|
Remote Indoor Sensor Fault | View Details |
| E222 |
Thermostat shows E222 indicating remote outdoor temperature sensor fault; outdoor temperature reading is missing or incorrect.
|
Outdoor Temperature Sensor Failure | View Details |
| E230 |
Thermostat displays E230 indicating humidity sensor fault; indoor humidity reading is unavailable or clearly wrong.
|
Internal Humidity Sensor Failure | View Details |
| E231 |
Thermostat shows E231 indicating remote humidity sensor fault (if a separate sensor is installed).
|
Remote Humidity Sensor Failure | View Details |
| E240 |
Thermostat displays E240 indicating Wi‑Fi connection failure; remote app control and cloud services are unavailable.
|
Wi‑Fi Connectivity Fault | View Details |
| E241 |
Thermostat shows E241 indicating loss of connection to Lennox cloud services; local control works but app access fails.
|
Cloud Service Communication Fault | View Details |
| E250 |
Thermostat displays E250 indicating configuration or equipment mismatch; system may not operate correctly.
|
System Configuration Error | View Details |
| E260 |
Thermostat shows E260 indicating internal memory or firmware error; may reboot repeatedly or lose settings.
|
Thermostat Firmware/Memory Fault | View Details |
| E270 |
Thermostat displays E270 indicating internal display or touch interface fault; screen may be blank, frozen, or unresponsive.
|
Display/Touchscreen Failure | View Details |
| E280 |
Thermostat shows E280 indicating internal fan control or G output fault; fan may not run when commanded.
|
Thermostat Fan Output Failure | View Details |
| E290 |
Thermostat displays E290 indicating dehumidification control fault; dehumidify function does not operate correctly.
|
Dehumidification Control Error | View Details |
| – |
Thermostat backlight flickers or display brightness changes unexpectedly.
|
Display Power Instability | View Details |
| – |
Thermostat calls for cooling but the air conditioner or heat pump does not start; fan may or may not run.
|
No Cooling Call Output | View Details |
| – |
Thermostat calls for heat but the furnace or heat pump does not start; no error code shown on thermostat.
|
No Heating Call Output | View Details |
| – |
Thermostat display is on but does not respond to touch or button presses.
|
Unresponsive Touchscreen | View Details |
| – |
Thermostat does not energize the fan in 'Fan On' mode, but fan runs during heating or cooling.
|
Fan-Only Control Failure | View Details |
| – |
Thermostat does not follow programmed schedule; temperature changes occur at wrong times or not at all.
|
Scheduling/Programming Fault | View Details |
| – |
Thermostat emits a burning smell or becomes unusually hot to the touch.
|
Overheating Thermostat Electronics | View Details |
| – |
Thermostat fails to control whole-home dehumidifier connected as a separate unit to Lennox system.
|
Standalone Dehumidifier Control Failure | View Details |
| – |
Thermostat fails to control whole-home humidifier connected to Lennox furnace/air handler.
|
Humidifier Control Failure | View Details |
| – |
Thermostat fails to control zoning properly; some zones do not heat/cool as commanded.
|
Zoning Control Misoperation | View Details |
| – |
Thermostat frequently disconnects from Wi‑Fi or Lennox app loses connection intermittently.
|
Intermittent Wi‑Fi Connectivity | View Details |
| – |
Thermostat is completely blank with no display and no response to touch or buttons.
|
No Power to Thermostat | View Details |
| – |
Thermostat loses date/time and custom settings after every power outage.
|
Loss of Non-Volatile Memory or Backup Power | View Details |
| – |
Thermostat reboots randomly several times a day without user input.
|
Intermittent Power or Firmware Reset | View Details |
| – |
Thermostat shows 'Equipment not responding' or similar message without a specific numeric code.
|
General Equipment Non-Response | View Details |
| – |
Thermostat shows 'Outdoor unit offline' but cooling still works intermittently.
|
Intermittent Outdoor Unit Communication | View Details |
| – |
Thermostat shows frequent 'Filter' or 'Service' reminders even after being reset.
|
Maintenance Reminder Configuration Issue | View Details |
| – |
Thermostat shows humidity reading that is clearly inaccurate compared to a known-good hygrometer.
|
Humidity Sensing Error | View Details |
| – |
Thermostat shows temperature that is clearly inaccurate compared to other thermometers in the home.
|
Temperature Sensing/Calibration Error | View Details |
No matching codes found
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