Carrier 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 communicate with the indoor unit; no system response to mode changes.
Indoor Unit Communication Fault
E10
Thermostat displays E10 and may not control zoning dampers correctly; some zones may not heat or cool.
Zoning Panel Communication Fault
E11
Thermostat displays E11 and may not respond to touch or may freeze intermittently.
User Interface / Touchscreen Fault
E12
Thermostat displays E12 and may show incorrect outdoor temperature or fail to optimize heat pump operation.
Outdoor Temperature Sensor Fault
E13
Thermostat displays E13 and may disable dehumidification or show erratic humidity control.
Dehumidifier Control Fault
E14
Thermostat displays E14 and may not control the humidifier; indoor humidity remains low despite calls for humidity.
Humidifier Control Fault
E15
Thermostat displays E15 and may not control ventilation; fresh air intake or ERV/HRV does not operate as expected.
Ventilation Control Fault
E16
Thermostat displays E16 and may not energize fan correctly; blower may not run or may run continuously.
Indoor Fan Control Fault
E17
Thermostat displays E17 and may not control second-stage heating or cooling; system may struggle to reach setpoint.
Second-Stage Control Fault
E18
Thermostat displays E18 and may show a persistent low battery or power error even when C-wire is present.
Thermostat Power Management Fault
E19
Thermostat displays E19 and may not complete initial setup or may lose configuration after power cycles.
Configuration / Memory Fault
E2
Thermostat displays E2 and system may shut down or run erratically; often associated with outdoor unit communication loss.
Outdoor Unit Communication Fault
E20
Thermostat displays E20 and may not control emergency heat correctly on heat pump systems.
Emergency Heat Control Fault
E3
Thermostat displays E3 and may show incorrect indoor temperature or fail to control system properly.
Indoor Temperature Sensor Fault
E4
Thermostat displays E4 and may show incorrect humidity readings or fail to control dehumidification/humidification.
Indoor Humidity Sensor Fault
E5
Thermostat displays E5 and system may not respond to heating or cooling calls; often indicates power or common wire issues.
Thermostat Power/Common Wire Fault
E6
Thermostat displays E6 and may not control auxiliary heat or heat pump correctly.
Heat Pump / Auxiliary Heat Configuration Fault
E7
Thermostat displays E7 and Wi‑Fi or cloud connectivity is lost; remote control via app fails.
Wi‑Fi / Cloud Communication Fault
E8
Thermostat displays E8 and may shut down heating or cooling due to detected high temperature at the thermostat or in the equipment.
Overtemperature Protection / High Temperature Fault
E9
Thermostat displays E9 and may disable certain functions; often associated with accessory modules like humidifiers or ventilators.
Accessory Module Communication Fault
Symptom
Thermostat and system short cycle, turning on and off frequently without reaching setpoint.
Short Cycling Due to Control or Sensor Issues
Symptom
Thermostat backlight flickers or display brightness changes when equipment starts.
Display Power Instability
Symptom
Thermostat calls for cooling, but outdoor unit does not start; indoor blower may run.
No Cooling Call Output
Symptom
Thermostat calls for heat, but furnace does not start; cooling and fan may still work.
No Heat Call Output
Symptom
Thermostat displays 'Filter' or maintenance reminder and may limit operation until reset.
Filter/Maintenance Reminder Lockout
Symptom
Thermostat does not detect or control installed Carrier humidifier, dehumidifier, or ERV/HRV.
Accessory Not Recognized by Thermostat
Symptom
Thermostat frequently reboots or restarts on its own, especially when heating or cooling starts.
Thermostat Voltage Drop / Brownout
Symptom
Thermostat indicates 'System Malfunction' or 'Call for Service' without a specific code, and system may be locked out.
General System Lockout Indication
Symptom
Thermostat is on, but HVAC system will not start in any mode (heat, cool, or fan).
No System Response to Thermostat Calls
Symptom
Thermostat is unresponsive to touch or buttons, but the display is lit.
Frozen User Interface
Symptom
Thermostat loses Wi‑Fi connection frequently or cannot stay connected to the Carrier app.
Intermittent Wi‑Fi Connectivity
Symptom
Thermostat randomly changes setpoints or schedules without user input.
Unexpected Schedule or Setpoint Changes
Symptom
Thermostat screen is completely blank and system does not respond to any inputs.
No Power to Thermostat
Symptom
Thermostat shows 'Aux Heat' or 'Emergency Heat' running frequently, even in mild weather.
Excessive Auxiliary Heat Usage
Symptom
Thermostat shows 'Cooling' or 'Heating' active, but room temperature changes very slowly or not at all.
Ineffective Temperature Control
Symptom
Thermostat shows temperature that is clearly inaccurate compared to the actual room temperature.
Thermostat Temperature Calibration Error
Symptom
Thermostat shows very high or very low indoor humidity readings that do not match actual conditions.
Humidity Sensor Misreading
Symptom
Thermostat time and date keep resetting after power interruptions.
Real-Time Clock / Backup Power Issue
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| E1 |
Thermostat displays E1 and will not communicate with the indoor unit; no system response to mode changes.
|
Indoor Unit Communication Fault | View Details |
| E10 |
Thermostat displays E10 and may not control zoning dampers correctly; some zones may not heat or cool.
|
Zoning Panel Communication Fault | View Details |
| E11 |
Thermostat displays E11 and may not respond to touch or may freeze intermittently.
|
User Interface / Touchscreen Fault | View Details |
| E12 |
Thermostat displays E12 and may show incorrect outdoor temperature or fail to optimize heat pump operation.
|
Outdoor Temperature Sensor Fault | View Details |
| E13 |
Thermostat displays E13 and may disable dehumidification or show erratic humidity control.
|
Dehumidifier Control Fault | View Details |
| E14 |
Thermostat displays E14 and may not control the humidifier; indoor humidity remains low despite calls for humidity.
|
Humidifier Control Fault | View Details |
| E15 |
Thermostat displays E15 and may not control ventilation; fresh air intake or ERV/HRV does not operate as expected.
|
Ventilation Control Fault | View Details |
| E16 |
Thermostat displays E16 and may not energize fan correctly; blower may not run or may run continuously.
|
Indoor Fan Control Fault | View Details |
| E17 |
Thermostat displays E17 and may not control second-stage heating or cooling; system may struggle to reach setpoint.
|
Second-Stage Control Fault | View Details |
| E18 |
Thermostat displays E18 and may show a persistent low battery or power error even when C-wire is present.
|
Thermostat Power Management Fault | View Details |
| E19 |
Thermostat displays E19 and may not complete initial setup or may lose configuration after power cycles.
|
Configuration / Memory Fault | View Details |
| E2 |
Thermostat displays E2 and system may shut down or run erratically; often associated with outdoor unit communication loss.
|
Outdoor Unit Communication Fault | View Details |
| E20 |
Thermostat displays E20 and may not control emergency heat correctly on heat pump systems.
|
Emergency Heat Control Fault | View Details |
| E3 |
Thermostat displays E3 and may show incorrect indoor temperature or fail to control system properly.
|
Indoor Temperature Sensor Fault | View Details |
| E4 |
Thermostat displays E4 and may show incorrect humidity readings or fail to control dehumidification/humidification.
|
Indoor Humidity Sensor Fault | View Details |
| E5 |
Thermostat displays E5 and system may not respond to heating or cooling calls; often indicates power or common wire issues.
|
Thermostat Power/Common Wire Fault | View Details |
| E6 |
Thermostat displays E6 and may not control auxiliary heat or heat pump correctly.
|
Heat Pump / Auxiliary Heat Configuration Fault | View Details |
| E7 |
Thermostat displays E7 and Wi‑Fi or cloud connectivity is lost; remote control via app fails.
|
Wi‑Fi / Cloud Communication Fault | View Details |
| E8 |
Thermostat displays E8 and may shut down heating or cooling due to detected high temperature at the thermostat or in the equipment.
|
Overtemperature Protection / High Temperature Fault | View Details |
| E9 |
Thermostat displays E9 and may disable certain functions; often associated with accessory modules like humidifiers or ventilators.
|
Accessory Module Communication Fault | View Details |
| – |
Thermostat and system short cycle, turning on and off frequently without reaching setpoint.
|
Short Cycling Due to Control or Sensor Issues | View Details |
| – |
Thermostat backlight flickers or display brightness changes when equipment starts.
|
Display Power Instability | View Details |
| – |
Thermostat calls for cooling, but outdoor unit does not start; indoor blower may run.
|
No Cooling Call Output | View Details |
| – |
Thermostat calls for heat, but furnace does not start; cooling and fan may still work.
|
No Heat Call Output | View Details |
| – |
Thermostat displays 'Filter' or maintenance reminder and may limit operation until reset.
|
Filter/Maintenance Reminder Lockout | View Details |
| – |
Thermostat does not detect or control installed Carrier humidifier, dehumidifier, or ERV/HRV.
|
Accessory Not Recognized by Thermostat | View Details |
| – |
Thermostat frequently reboots or restarts on its own, especially when heating or cooling starts.
|
Thermostat Voltage Drop / Brownout | View Details |
| – |
Thermostat indicates 'System Malfunction' or 'Call for Service' without a specific code, and system may be locked out.
|
General System Lockout Indication | View Details |
| – |
Thermostat is on, but HVAC system will not start in any mode (heat, cool, or fan).
|
No System Response to Thermostat Calls | View Details |
| – |
Thermostat is unresponsive to touch or buttons, but the display is lit.
|
Frozen User Interface | View Details |
| – |
Thermostat loses Wi‑Fi connection frequently or cannot stay connected to the Carrier app.
|
Intermittent Wi‑Fi Connectivity | View Details |
| – |
Thermostat randomly changes setpoints or schedules without user input.
|
Unexpected Schedule or Setpoint Changes | View Details |
| – |
Thermostat screen is completely blank and system does not respond to any inputs.
|
No Power to Thermostat | View Details |
| – |
Thermostat shows 'Aux Heat' or 'Emergency Heat' running frequently, even in mild weather.
|
Excessive Auxiliary Heat Usage | View Details |
| – |
Thermostat shows 'Cooling' or 'Heating' active, but room temperature changes very slowly or not at all.
|
Ineffective Temperature Control | View Details |
| – |
Thermostat shows temperature that is clearly inaccurate compared to the actual room temperature.
|
Thermostat Temperature Calibration Error | View Details |
| – |
Thermostat shows very high or very low indoor humidity readings that do not match actual conditions.
|
Humidity Sensor Misreading | View Details |
| – |
Thermostat time and date keep resetting after power interruptions.
|
Real-Time Clock / Backup Power Issue | View Details |
No matching codes found
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