Lux
Lux 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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E1
Thermostat displays E1 and will not control heating or cooling
Room Temperature Sensor Open Circuit
E10
Thermostat displays E10 and system will not respond to mode changes
HVAC Control Relay Drive Fault
E11
Thermostat displays E11 and heat pump reversing valve will not energize correctly
O/B Reversing Valve Output Fault
E12
Thermostat displays E12 and fan will not respond to commands
G Fan Output Fault
E13
Thermostat displays E13 and will not energize compressor (Y output)
Compressor Stage 1 Output Fault
E14
Thermostat displays E14 and second-stage heat or cool will not engage
Stage 2 Output Fault (W2/Y2)
E15
Thermostat displays E15 and touchscreen does not respond reliably
Touchscreen Calibration or Hardware Fault
E16
Thermostat displays E16 and backlight or display fails intermittently
Display Power or Backlight Driver Fault
E17
Thermostat displays E17 and schedules or settings are lost unexpectedly
Non-Volatile Memory Write Failure
E18
Thermostat displays E18 and cannot detect or pair with Bluetooth setup device (on models using BLE for initial setup)
Bluetooth Module Fault
E19
Thermostat displays E19 and geofencing or location-based features do not function
Location Services or Time Sync Error
E2
Thermostat displays E2 and shows incorrect or no temperature reading
Room Temperature Sensor Short Circuit
E20
Thermostat displays E20 and refuses to start heating or cooling due to safety lockout
Compressor/Heat Pump Short-Cycle Lockout
E3
Thermostat displays E3 and will not control the system correctly
External Remote Sensor Open Circuit
E4
Thermostat displays E4 and may lock out heating or cooling
External Remote Sensor Short Circuit
E5
Thermostat displays E5 and Wi‑Fi or app connectivity is unavailable
Wi‑Fi Module Communication Failure
E6
Thermostat displays E6 and cannot complete cloud/app registration
Cloud Service Authentication Error
E7
Thermostat displays E7 and screen may freeze or reboot repeatedly
Internal Memory or Firmware Corruption
E8
Thermostat displays E8 and backlight may flicker or dim
Low 24VAC Supply Voltage
E9
Thermostat displays E9 and will not power up fully or reboots when calling for heat/cool
C‑Wire Power Loss or Insufficient Power
Symptom
Thermostat backlight is very dim or flickers but unit otherwise works
Backlight Degradation or Power Instability
Symptom
Thermostat buttons or touchscreen areas do not respond or respond intermittently
User Interface Input Failure
Symptom
Thermostat calls for cooling but only the indoor blower runs; outdoor unit does not start
Cooling Call Not Reaching Condenser
Symptom
Thermostat calls for heat but only the fan runs and no warm air is produced
Heat Call Not Reaching Burner or Heat Strips
Symptom
Thermostat does not follow programmed schedule or randomly changes setpoints
Scheduling or Program Execution Fault
Symptom
Thermostat does not respond to geofencing or away/home automation as expected
Geofencing Behavior Issue
Symptom
Thermostat emits a buzzing or humming noise, especially when calling for heat or cool
Electrical Noise or Relay Vibration
Symptom
Thermostat fails to control auxiliary or emergency heat on a heat pump system
Aux/E Heat Control Failure
Symptom
Thermostat fails to update time automatically or shows incorrect time after power interruptions
Timekeeping or NTP Sync Issue
Symptom
Thermostat frequently overshoots the set temperature, causing rooms to become too hot or too cold
Poor Temperature Control or Overshoot
Symptom
Thermostat has power but will not turn on heat when temperature is set higher than room temperature
No Heat Call from Thermostat
Symptom
Thermostat plastic housing feels unusually warm to the touch
Internal Overheating or High Load on Power Circuit
Symptom
Thermostat rapidly turns the system on and off (short cycling)
Short Cycling Due to Control Settings or Sensor Placement
Symptom
Thermostat reboots or resets when heating or cooling starts
Voltage Sag or Electrical Noise on 24VAC Supply
Symptom
Thermostat screen is completely blank and unit appears dead
No 24VAC Power to Thermostat
Symptom
Thermostat temperature reading is significantly higher or lower than actual room temperature
Room Temperature Sensing Error
Symptom
Thermostat will not start cooling even though it is set to COOL and the setpoint is below room temperature
No Cooling Call from Thermostat
Symptom
Thermostat Wi‑Fi connection drops frequently or app shows thermostat offline
Intermittent Wi‑Fi Connectivity
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E1 |
Thermostat displays E1 and will not control heating or cooling
|
Room Temperature Sensor Open Circuit | View Details |
| E10 |
Thermostat displays E10 and system will not respond to mode changes
|
HVAC Control Relay Drive Fault | View Details |
| E11 |
Thermostat displays E11 and heat pump reversing valve will not energize correctly
|
O/B Reversing Valve Output Fault | View Details |
| E12 |
Thermostat displays E12 and fan will not respond to commands
|
G Fan Output Fault | View Details |
| E13 |
Thermostat displays E13 and will not energize compressor (Y output)
|
Compressor Stage 1 Output Fault | View Details |
| E14 |
Thermostat displays E14 and second-stage heat or cool will not engage
|
Stage 2 Output Fault (W2/Y2) | View Details |
| E15 |
Thermostat displays E15 and touchscreen does not respond reliably
|
Touchscreen Calibration or Hardware Fault | View Details |
| E16 |
Thermostat displays E16 and backlight or display fails intermittently
|
Display Power or Backlight Driver Fault | View Details |
| E17 |
Thermostat displays E17 and schedules or settings are lost unexpectedly
|
Non-Volatile Memory Write Failure | View Details |
| E18 |
Thermostat displays E18 and cannot detect or pair with Bluetooth setup device (on models using BLE for initial setup)
|
Bluetooth Module Fault | View Details |
| E19 |
Thermostat displays E19 and geofencing or location-based features do not function
|
Location Services or Time Sync Error | View Details |
| E2 |
Thermostat displays E2 and shows incorrect or no temperature reading
|
Room Temperature Sensor Short Circuit | View Details |
| E20 |
Thermostat displays E20 and refuses to start heating or cooling due to safety lockout
|
Compressor/Heat Pump Short-Cycle Lockout | View Details |
| E3 |
Thermostat displays E3 and will not control the system correctly
|
External Remote Sensor Open Circuit | View Details |
| E4 |
Thermostat displays E4 and may lock out heating or cooling
|
External Remote Sensor Short Circuit | View Details |
| E5 |
Thermostat displays E5 and Wi‑Fi or app connectivity is unavailable
|
Wi‑Fi Module Communication Failure | View Details |
| E6 |
Thermostat displays E6 and cannot complete cloud/app registration
|
Cloud Service Authentication Error | View Details |
| E7 |
Thermostat displays E7 and screen may freeze or reboot repeatedly
|
Internal Memory or Firmware Corruption | View Details |
| E8 |
Thermostat displays E8 and backlight may flicker or dim
|
Low 24VAC Supply Voltage | View Details |
| E9 |
Thermostat displays E9 and will not power up fully or reboots when calling for heat/cool
|
C‑Wire Power Loss or Insufficient Power | View Details |
| – |
Thermostat backlight is very dim or flickers but unit otherwise works
|
Backlight Degradation or Power Instability | View Details |
| – |
Thermostat buttons or touchscreen areas do not respond or respond intermittently
|
User Interface Input Failure | View Details |
| – |
Thermostat calls for cooling but only the indoor blower runs; outdoor unit does not start
|
Cooling Call Not Reaching Condenser | View Details |
| – |
Thermostat calls for heat but only the fan runs and no warm air is produced
|
Heat Call Not Reaching Burner or Heat Strips | View Details |
| – |
Thermostat does not follow programmed schedule or randomly changes setpoints
|
Scheduling or Program Execution Fault | View Details |
| – |
Thermostat does not respond to geofencing or away/home automation as expected
|
Geofencing Behavior Issue | View Details |
| – |
Thermostat emits a buzzing or humming noise, especially when calling for heat or cool
|
Electrical Noise or Relay Vibration | View Details |
| – |
Thermostat fails to control auxiliary or emergency heat on a heat pump system
|
Aux/E Heat Control Failure | View Details |
| – |
Thermostat fails to update time automatically or shows incorrect time after power interruptions
|
Timekeeping or NTP Sync Issue | View Details |
| – |
Thermostat frequently overshoots the set temperature, causing rooms to become too hot or too cold
|
Poor Temperature Control or Overshoot | View Details |
| – |
Thermostat has power but will not turn on heat when temperature is set higher than room temperature
|
No Heat Call from Thermostat | View Details |
| – |
Thermostat plastic housing feels unusually warm to the touch
|
Internal Overheating or High Load on Power Circuit | View Details |
| – |
Thermostat rapidly turns the system on and off (short cycling)
|
Short Cycling Due to Control Settings or Sensor Placement | View Details |
| – |
Thermostat reboots or resets when heating or cooling starts
|
Voltage Sag or Electrical Noise on 24VAC Supply | View Details |
| – |
Thermostat screen is completely blank and unit appears dead
|
No 24VAC Power to Thermostat | View Details |
| – |
Thermostat temperature reading is significantly higher or lower than actual room temperature
|
Room Temperature Sensing Error | View Details |
| – |
Thermostat will not start cooling even though it is set to COOL and the setpoint is below room temperature
|
No Cooling Call from Thermostat | View Details |
| – |
Thermostat Wi‑Fi connection drops frequently or app shows thermostat offline
|
Intermittent Wi‑Fi Connectivity | View Details |
No matching codes found
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