Honeywell Home
Honeywell Home 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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Aux Heat Not Responding
Heat pump system does not engage auxiliary or emergency heat when needed
Auxiliary Heat Stage Control Failure
Battery Low
Thermostat displays 'Battery Low' or shows a low‑battery icon
Low Backup Battery Voltage
Cool Not Responding
App or thermostat shows 'Cool Not Responding' and AC does not run
Failed Cooling Call from Thermostat to Equipment
Cool On Flashing
Display shows 'Cool On' flashing and AC does not start
Compressor Short‑Cycle Protection / Minimum Off Timer
E1
Thermostat displays E1 and will not control heating or cooling
Indoor Temperature Sensor Open Circuit
E2
Thermostat displays E2 and temperature reading is inaccurate or blank
Indoor Temperature Sensor Short Circuit
E3
Thermostat displays E3 and may not control system correctly
Outdoor Temperature Sensor Open Circuit
E4
Thermostat displays E4 and may show incorrect outdoor temperature
Outdoor Temperature Sensor Short Circuit
E42
Thermostat displays E42 and cannot connect to Wi‑Fi
Wi‑Fi DHCP or IP Address Assignment Failure
E43
Thermostat displays E43 and shows no internet connection
Wi‑Fi Router Not Connected to Internet
E5
Thermostat displays E5 and system will not run or runs erratically
Internal Thermostat Power or Voltage Error
E99
Thermostat displays E99 and is unresponsive or stuck
Internal Firmware or Hardware Failure
Heat Not Responding
App or thermostat shows 'Heat Not Responding' and home does not warm up
Failed Heat Call from Thermostat to Equipment
Heat On Flashing
Display shows 'Heat On' flashing and furnace does not start
Burner Short‑Cycle Protection / Minimum Off Timer
No Power to Thermostat
Honeywell Home smart thermostat screen is blank or dark and unresponsive
Loss of 24VAC Control Power
No Signal
Wireless Honeywell Home smart thermostat shows 'No Signal' or 'Lost Connection' to wireless receiver or RedLINK gateway
Wireless Communication Loss
Schedule Error
Thermostat behaves unpredictably due to corrupted or conflicting schedule settings
Internal Schedule Configuration Fault
Sensor Error
Thermostat or app reports 'Sensor Error' for a remote room sensor
Remote Room Sensor Communication or Circuit Fault
Wi‑Fi Icon Blinking
Wi‑Fi icon on Honeywell Home smart thermostat blinks and app cannot control thermostat
Intermittent Wi‑Fi Connection
Symptom
Thermostat backplate or wiring shows signs of corrosion or rust
Environmental Damage to Low‑Voltage Connections
Symptom
Thermostat calls for cooling but AC short cycles (frequent on/off, poor dehumidification)
Cooling Short Cycling / Improper Cycle Rate
Symptom
Thermostat calls for heat but furnace short cycles (turns on and off frequently)
Short Cycling Due to Incorrect Cycle Rate or Oversized System
Symptom
Thermostat cannot be added to Honeywell Home / Resideo app (pairing fails)
Provisioning or Registration Failure
Symptom
Thermostat cannot control humidifier or dehumidifier as expected
Accessory Control Configuration or Wiring Fault
Symptom
Thermostat clicks but furnace or AC does not start
Thermostat Relay Operating but No 24VAC Output to Equipment
Symptom
Thermostat display is dim, flickering, or touch response is erratic
Display Backlight or Touchscreen Failure
Symptom
Thermostat does not follow programmed schedule (stays at one temperature)
Hold Mode or Schedule Override Active
Symptom
Thermostat does not turn on fan in Auto mode even though heating or cooling is running
Fan Control Configuration or G‑Wire Issue
Symptom
Thermostat fan runs continuously even when set to Auto and no call for heat/cool
Stuck Fan Relay or Miswired G Circuit
Symptom
Thermostat frequently disconnects from Honeywell Home / Resideo cloud (app shows offline)
Cloud Connectivity Instability
Symptom
Thermostat loses time or date settings after power outages
Real‑Time Clock or Backup Power Issue
Symptom
Thermostat or surrounding wall feels unusually warm to the touch
Internal Heat from Electronics or Wall Cavity Heat
Symptom
Thermostat randomly reboots or restarts during operation
Intermittent Power or Firmware Instability
Symptom
Thermostat shows 'Waiting for Equipment' for an extended period
Equipment Protection Delay or Safety Lockout
Symptom
Thermostat shows heat or cool is on, but room temperature never reaches setpoint
System Capacity or Runtime Issue
Symptom
Thermostat temperature reading is inaccurate compared to other thermometers
Temperature Calibration or Sensor Drift
| Error Code | Symptom | Fault Type | Guide |
|---|---|---|---|
| Aux Heat Not Responding |
Heat pump system does not engage auxiliary or emergency heat when needed
|
Auxiliary Heat Stage Control Failure | View Details |
| Battery Low |
Thermostat displays 'Battery Low' or shows a low‑battery icon
|
Low Backup Battery Voltage | View Details |
| Cool Not Responding |
App or thermostat shows 'Cool Not Responding' and AC does not run
|
Failed Cooling Call from Thermostat to Equipment | View Details |
| Cool On Flashing |
Display shows 'Cool On' flashing and AC does not start
|
Compressor Short‑Cycle Protection / Minimum Off Timer | View Details |
| E1 |
Thermostat displays E1 and will not control heating or cooling
|
Indoor Temperature Sensor Open Circuit | View Details |
| E2 |
Thermostat displays E2 and temperature reading is inaccurate or blank
|
Indoor Temperature Sensor Short Circuit | View Details |
| E3 |
Thermostat displays E3 and may not control system correctly
|
Outdoor Temperature Sensor Open Circuit | View Details |
| E4 |
Thermostat displays E4 and may show incorrect outdoor temperature
|
Outdoor Temperature Sensor Short Circuit | View Details |
| E42 |
Thermostat displays E42 and cannot connect to Wi‑Fi
|
Wi‑Fi DHCP or IP Address Assignment Failure | View Details |
| E43 |
Thermostat displays E43 and shows no internet connection
|
Wi‑Fi Router Not Connected to Internet | View Details |
| E5 |
Thermostat displays E5 and system will not run or runs erratically
|
Internal Thermostat Power or Voltage Error | View Details |
| E99 |
Thermostat displays E99 and is unresponsive or stuck
|
Internal Firmware or Hardware Failure | View Details |
| Heat Not Responding |
App or thermostat shows 'Heat Not Responding' and home does not warm up
|
Failed Heat Call from Thermostat to Equipment | View Details |
| Heat On Flashing |
Display shows 'Heat On' flashing and furnace does not start
|
Burner Short‑Cycle Protection / Minimum Off Timer | View Details |
| No Power to Thermostat |
Honeywell Home smart thermostat screen is blank or dark and unresponsive
|
Loss of 24VAC Control Power | View Details |
| No Signal |
Wireless Honeywell Home smart thermostat shows 'No Signal' or 'Lost Connection' to wireless receiver or RedLINK gateway
|
Wireless Communication Loss | View Details |
| Schedule Error |
Thermostat behaves unpredictably due to corrupted or conflicting schedule settings
|
Internal Schedule Configuration Fault | View Details |
| Sensor Error |
Thermostat or app reports 'Sensor Error' for a remote room sensor
|
Remote Room Sensor Communication or Circuit Fault | View Details |
| Wi‑Fi Icon Blinking |
Wi‑Fi icon on Honeywell Home smart thermostat blinks and app cannot control thermostat
|
Intermittent Wi‑Fi Connection | View Details |
| – |
Thermostat backplate or wiring shows signs of corrosion or rust
|
Environmental Damage to Low‑Voltage Connections | View Details |
| – |
Thermostat calls for cooling but AC short cycles (frequent on/off, poor dehumidification)
|
Cooling Short Cycling / Improper Cycle Rate | View Details |
| – |
Thermostat calls for heat but furnace short cycles (turns on and off frequently)
|
Short Cycling Due to Incorrect Cycle Rate or Oversized System | View Details |
| – |
Thermostat cannot be added to Honeywell Home / Resideo app (pairing fails)
|
Provisioning or Registration Failure | View Details |
| – |
Thermostat cannot control humidifier or dehumidifier as expected
|
Accessory Control Configuration or Wiring Fault | View Details |
| – |
Thermostat clicks but furnace or AC does not start
|
Thermostat Relay Operating but No 24VAC Output to Equipment | View Details |
| – |
Thermostat display is dim, flickering, or touch response is erratic
|
Display Backlight or Touchscreen Failure | View Details |
| – |
Thermostat does not follow programmed schedule (stays at one temperature)
|
Hold Mode or Schedule Override Active | View Details |
| – |
Thermostat does not turn on fan in Auto mode even though heating or cooling is running
|
Fan Control Configuration or G‑Wire Issue | View Details |
| – |
Thermostat fan runs continuously even when set to Auto and no call for heat/cool
|
Stuck Fan Relay or Miswired G Circuit | View Details |
| – |
Thermostat frequently disconnects from Honeywell Home / Resideo cloud (app shows offline)
|
Cloud Connectivity Instability | View Details |
| – |
Thermostat loses time or date settings after power outages
|
Real‑Time Clock or Backup Power Issue | View Details |
| – |
Thermostat or surrounding wall feels unusually warm to the touch
|
Internal Heat from Electronics or Wall Cavity Heat | View Details |
| – |
Thermostat randomly reboots or restarts during operation
|
Intermittent Power or Firmware Instability | View Details |
| – |
Thermostat shows 'Waiting for Equipment' for an extended period
|
Equipment Protection Delay or Safety Lockout | View Details |
| – |
Thermostat shows heat or cool is on, but room temperature never reaches setpoint
|
System Capacity or Runtime Issue | View Details |
| – |
Thermostat temperature reading is inaccurate compared to other thermometers
|
Temperature Calibration or Sensor Drift | View Details |
No matching codes found
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