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Decoding the meaning of a new error code that suddenly pops up on your Honeywell thermostat can be a bit difficult.

These error codes usually indicate a hardware fault but can also relate to Wi-Fi issues or incorrect settings.

To help you understand what they mean, I’ve created this guide where I provide a full list of error codes common across all Honeywell thermostats to help you troubleshoot. I also provide a list of model-specific error codes for the newer smart thermostats.

So keep reading to learn what they are and how to fix them.

What are Error Codes?

Since most thermostats don’t use sophisticated displays, error codes help map out all the different issues that your thermostat can run into.

By understanding the meaning behind these codes displayed on your thermostat, you can address the issue and resolve it.

Are Error Codes Specific to the Model or Manufacturer?

Error codes vary by manufacturer, but for Honeywell thermostats, many codes are consistent across multiple models.

Combined List of Honeywell Thermostat Error Codes 

Error codes can help diagnose most issues with your Honeywell Smart thermostat. So, here's a breakdown of all the most common Honeywell thermostat error codes.

54Problem: Error in the Thermostat Humidity Sensor
Details: The sensor of the thermostat has encountered an error. Contact the installer or HVAC professional.
164Problem: Heat Pump Issue
Details: This indicates a problem with the heat pump. It most likely needs servicing. It's best to contact your HVAC technician.
168Problem: Wi-Fi Radio Faulty
Details: This shows that the Wi-Fi module is not working and wireless connectivity is not available. Contact your HVAC technician for help.
170Problem: Internal Memory  Error
Details: The internal memory card of the thermostat has encountered an error. Please contact your HVAC technician. The memory chip might need to be replaced.
171Problem: Date and Time are Not Set
Details: Reminds you to set the correct date and time to make use of presets/programs and scheduling.
173Problem: Error with the Temperature Sensor
Details: This indicates that the embedded temperature sensor is not working. Contact your HVAC technician for repairs/replacement
175Problem: AC Power Delay
Details: Usually displayed after a power outage or blackout. Indicates that the AC power has resumed operation. You don’t have to take any action. 
177Problem: Indoor Temperature Sensor Faulty
Details: The indoor temperature sensor of the thermostat is either disconnected or not wired properly. Seek assistance from an HVAC professional.
178Problem: Outdoor Temperature Sensor Faulty
Details: The outdoor temperature sensor of the thermostat is either disconnected or not wired properly. Seek assistance from your HVAC professional.
181/182Problem: Air Filter Clogged
Details: The air filter should be replaced. Contact a professional HVAC technician. You can dismiss this error code once you’ve replaced the filter.
183Problem: Humidifier Tank and Water Filter Clog
Details: The humidifier tank needs a thorough cleaning and the water filter needs to be replaced. You can clean it yourself or get help from an HVAC technician.
184Problem: Humidifier Pad Blockage
Details: You need to replace the humidifier pad. You can DIY it or a professional HVAC technician can get it done for you. 
185Problem: Dehumidifier Filter Blocked
Details: This error indicates that you need to replace the dehumidifier filter. DIY it or contact an HVAC technician. 
186Problem: Ventilator Core Needs Cleaning
Details: You need to clean the ventilator core. You can DIY it or get help from a pro
187Problem: The Ventilator Filter is Clogged
Details: The ventilator filter needs cleaning/replacing. DIY or contact a professional.
188/189Problem: UV Bulb Defective
Details: You need to replace the UV bulb. Do it yourself or get an HVAC technician to help. 
210Problem: Online Registration for Outdoor Temperature Not Successful
Details:  Shows that you still haven’t completed the online registration. If you want to get up-to-date outdoor weather temperatures, you need to get the Thermostat connected and register online. This can be done through the mobile app.
252Problem: AC Power Lost 
Details: (Only for Z-Wave models) Indicates power failure and reminds you to restore the connection as soon as possible since the batteries will be used as backup power, draining them faster, especially with the Z-Wave communication network being turned on. 
388Problem: Online Registration for Remote Access and Outdoor Temperature Still Not Complete
Details:  Reminder to register your thermostat via the mobile app. This will allow you to remotely access your temperature and also get access to accurate outdoor temperatures.
399Problem: Wi-Fi Radio Faulty
Details: It shows that the Wi-Fi module is not working and wireless connectivity is not available. Contact your HVAC technician for help.
400Problem: No Wi-Fi Signal 
Details: The thermostat can’t read a Wi-Fi signal. Wait for the thermostat to reconnect or select a new Wi-Fi network.
405Problem: Battery Low 
Details: Batteries are running low. Turn off the system safely andreplace the batteries.
407Problem: Battery Low 
Details: Batteries are running low. Turn off the system safely and replace the batteries.
508Problem: Wi-Fi Connection is Not Yet Configured 
Details: Download the Honeywell Home app and follow the steps to link your thermostat to your Wi-Fi network.
546Problem: (For Z-Wave models) Z-Wave Not Configured
Details: The thermostat has not yet been configured to receive commands from your Z-Wave network. Check the user guide to enroll the thermostat to your Z-Wave network.
547Problem: Z-Wave Radio Malfunction
Details: Z-Wave module is not working and the thermostat cannot receive commands from your Z-Wave network. Contact an installer or HVAC professional to replace the thermostat. 
E1/E2Problem: Z-Wave Radio Malfunction
Details: The Z-Wave module is not working and the thermostat cannot receive commands from your Z-Wave network. Contact an installer or HVAC professional to replace the thermostat. 
E01Problem: Wi-Fi Setup Error
Details: Make sure your router is connected to a power source and is within signal range while trying to connect your thermostat to the Wi-Fi network.
E02Problem: Invalid Wi-Fi password
Details: Pops up when you’ve entered an invalid Wi-Fi password. Try again with the correct code or try changing your Wi-Fi password.
E42Problem: IP address Issue
Details: This error usually comes in when there’s an issue with the Wi-Fi router’s automatic IP assigning feature. Make sure the router is properly set up.
E43Problem:  Problem communicating with Total Connect Comfort App
Details: Your Internet connection has been lost and the thermostat cannot connect to the Total Connect Comfort app. Check with your internet provider or try again after making sure your Wi-Fi network can connect to the internet.
E99Problem: General error
Details: Indicates a general initialization or configuration error. Remove the thermostat and reconnect it after several minutes.
Table for the combined list of Honeywell error codes

Model-Specific Error Codes

While the previous list covers all common Honeywell thermostat error codes, certain codes may be exclusive to specific models.

If your model is listed below, you can check the unique model-specific error codes right below. However, if you can’t find a specific model, you can refer to this article which contains an index of all Honeywell Thermostat manuals.

T10 Pro and T9

Honeywell has gotten rid of the error codes with the more recent models. Instead of error codes, the smart thermostat now pushes alerts with detailed error messages.

For these models, the red dot above the Menu icon will usually indicate any active alert or notification. Unlike the numbered error codes, these alerts will include detailed messages and provide you with instructions on how to resolve them.

To Access Alerts and Notifications: 

  1. Touch the Menu icon.
  2. Go to “Notifications” 
  3. A list of recent notifications will pop up.
  4. Touch any of these alert messages/notifications to get more details.
Honeywell T10 Pro Alert Screen
How to access alerts and notifications in the Honeywell T10 Pro smart model

Error Messages Common to T9 and T10 Models

Here are the most common error messages and solutions to fix them.

  • “Set Date and Time”: The date and time have not been configured yet. Press on this alert and follow the on-screen instructions to set up the correct date and time.
  • “Wi-Fi Module Error”: Wi-Fi module has failed. Attempt a restart or replace the Wi-Fi module.
  • “Need to Register Online”: Add your thermostat in the Honeywell Home App.
  • “No Internet Connection”: Check your router and modem for signal issues and internet connectivity.
  • “Wi-Fi Signal Lost”: Reconnect or choose a different network by following on-screen instructions.
  • “Wi-Fi Not Configured”: Connect or disable Wi-Fi through on-screen settings.
  • “Internet Required for Outdoor Temperature”: Connect the thermostat to the internet by following the on-screen steps.
  • “Power Restored”: No action is needed. Just reminding you that the power interruption was resolved.
  • “Heat Pump Failure”: Heat Pump is not responding. Call a contractor to diagnose and service the heat pump.
  • “Memory Error”/”Thermostat Memory Error”: Memory chip failure. Replace the thermostat.
  • Internal Sensor Error”: The Embedded sensor in the thermostat is defective. Replace the thermostat.
  • “Internal Hum Temp Failure”: Replace the thermostat due to failure in the internal humidity or the temperature sensor.
  • “Thermostat Unknown Time”: Reset the time or verify the Wi-Fi connection. Make sure the Wi-Fi can connect to the internet.
  • “Low Sensor Batteries”: Batteries are running low. Replace the AAA Alkaline batteries on the thermostat.
  • “Indoor Sensor Error”: Indoor temperature sensor is defective. Replace the indoor sensor.
  • “Indoor Sensor Connection Error”: Trouble Connecting to the Indoor Sensor. Replace batteries and reposition the sensor.

Below are some more unusual error messages you may encounter with these models.

Error MessageIssueSolution
Outdoor Sensor ErrorThe outdoor temperature sensor is not detected.Check the outdoor sensor and wiring.
Floor Temperature Sensor ErrorThe floor temperature sensor is not connecting or seems to be defective.Check the floor sensor and its wiring. However, please note that this sensor is yet to be implemented.
Wired Indoor Temp Sensor FailureThe indoor temperature sensor is not detected.Check the indoor sensor and wiring.
Wired Outdoor Temp Sensor FailureThe wired outdoor temperature sensor is not detected.Check the outdoor sensor and wiring.
RedLINK RF Toolkit Not RespondingThe wireless sensor RF network is not operating, and the wireless sensor features are unavailable.Contact Customer Care for assistance; this error may stem from a faulty radio or disconnected connection between the thermostat and the radio.
Table outlining the error messages common to T9 and T10 Honeywell Smart Thermostats

T6 Pro Smart

For the T6 Pro Smart and similar models, the touchscreen will show up a “general warning” sign to indicate any errors or alerts.

Honeywell T6 Pro Screen Alert Icon 1
Alert sign on the Honeywell T6 Pro Smart Models

To access these alerts or messages:

  1. Touch on the “Menu”
  2. Use the “+” or “-” buttons until you get to the “ALERTS” sub-menu.
  3. From there, touch on “Select” to open the alerts screen
  4. The 3-digit error code will show up along with a description when you scroll down
  5. You can use the left or right arrows or + and – buttons to scroll between multiple alerts and dismiss the unimportant ones.

Unique Error Codes for the T6 Pro Smart

400: Indicates a loss of Wi-Fi Signal. Give it some time to reconnect or choose another network.

508: Notifies that the Wi-Fi is not yet configured. Make sure to download the Honeywell Home app and follow the provided instructions to link your thermostat.

T6 Pro Z-Wave

For the Z-Wave model, a couple of extra unique error codes can pop up. These are: 

54: Indicates that the humidity sensor on your thermostat has malfunctioned and needs to be replaced.

252: Alerts you whenever the thermostat switches to power-save mode (LSS) or when AC power is restored. This notifies you to re-establish the mains power as soon as possible so you can prevent unnecessary battery drainage because of the Z-Wave network.


Unless you’ve got the error codes taped beside your thermostat, figuring out what they mean can be tedious. 

However, as long as you’re taking care of the entire HVAC system and ensuring the thermostat doesn’t run into signal issues, you won’t encounter these error codes as much. 

Hopefully, this article helped you determine what’s wrong. If you encounter any more error codes in the future, don’t forget to check back with this article.


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