Honeywell Home thermostat error codes
It depends on the model. T6 Pro and FocusPRO S200 thermostats show numbered alerts, such as 164 for a heat pump fault or 173 for a failed internal sensor. FocusPRO Wi-Fi models show codes such as E02 and E42 for Wi-Fi setup problems. T9 and T10 thermostats spell the alert out in words.
Why do Honeywell codes look so different from model to model?
Because each product family uses its own system. There is no single Honeywell Home code list. The T6 Pro and FocusPRO S200 show a number, the FocusPRO Wi-Fi Series shows a letter E and two digits, and the touchscreen T9 and T10 write the alert out in capital letters. A code that means one thing on one family can be missing or mean nothing on another.
So the first step is to find your model name. It is printed on the cover of the user guide that came with the thermostat. Then use the matching table below. Every meaning here is copied from Honeywell's own documentation for that family, listed under Sources.
What do the numbered T6 Pro alert codes mean?
When a T6 Pro has an alert or reminder, an alert icon appears on the home screen. To see the code, press Menu and then the arrow until the display shows "ALRT", then press Select.
| Code | Honeywell's meaning | Who handles it |
|---|---|---|
| 164 | The L terminal is energized at the equipment: the heat pump is telling the thermostat there is a problem with the heat pump | Licensed HVAC technician |
| 170 | Memory failure. Replace the thermostat | A replacement thermostat, installed by a licensed HVAC technician |
| 171 | Reminder to set the date and time | You, on the thermostat |
| 173 | Replace the thermostat because of an internal sensor failure | A replacement thermostat, installed by a licensed HVAC technician |
| 177 | Invalid reading on a wired indoor sensor (not on the TH6210U) | Licensed HVAC technician |
| 178 | Invalid reading on a wired outdoor sensor (not on the TH6210U) | Licensed HVAC technician |
| 181 | "Replace Filter 1" reminder, set by the installer | You, then clear it on the thermostat |
| 182 | "Replace Filter 2" reminder, set by the installer | You, then clear it on the thermostat |
| 405 | "Low Battery": replace the AA batteries ("BATT" also shows) | You |
| 407 | "Critically Low Battery": replace the AA batteries | You |
The two filter codes are explained on our page about the filter reminder, and the battery codes on low battery messages. Honeywell adds that some alerts cannot be snoozed or cleared, and that if that happens you should call a heating and cooling professional because the system may need service.
What do the FocusPRO S200 alert numbers mean?
The FocusPRO S200 Series (TH2110WF4008, TH2320WF4010, TH2320WF4011) uses some of the same numbers as the T6 Pro and adds Wi-Fi alerts. Press MENU and scroll until the alert shows, then press SELECT to see the number. Honeywell says an alert cannot be dismissed on this model.
| Alert number | Honeywell's meaning |
|---|---|
| 164 | Heat pump fault: the heat pump is energizing the L terminal to indicate a fault |
| 170 | Thermostat memory failure |
| 171 | Set time and date |
| 173 | Internal sensor error: issue with the built-in temperature sensor |
| 178 | Wired outdoor sensor error |
| 388 | Register online |
| 399 | Wi-Fi internet connection lost |
| 400 | Wi-Fi no signal |
| 602 | Internal humidity sensor error |
| 607 | Wi-Fi network error |
Honeywell says some of these can be resolved by the homeowner and others may need a service call to the installer. The Wi-Fi alerts are the ones you can usually work on yourself; our page on a thermostat that has gone offline covers them.
What do E01, E02, E42, E43 and E99 mean?
These come from the FocusPRO TH6320WF1005 Wi-Fi Series. Its guide says error codes first show alone in the time area of the screen, and after a few minutes the code alternates with the time.
| Code | Honeywell's meaning | Honeywell's suggested action |
|---|---|---|
| E01 | During Wi-Fi setup, the router lost power | Make sure the router has power |
| E02 | Invalid Wi-Fi password. Shows for 30 seconds, then the thermostat re-enters Wi-Fi setup | Re-enter the password for your home Wi-Fi network |
| E42 | The router is not issuing an IP address to the thermostat | Wait 30 minutes; if still not connected, remove the thermostat from its wallplate for 10 seconds and reconnect it |
| E43 | No internet connection; the thermostat cannot reach Total Connect Comfort | Reboot the router |
| E99 | General error | Remove the thermostat from its wallplate for 10 seconds, then reconnect it |
None of these codes points to the heating or cooling equipment. They are all about the thermostat's connection to your network.
What do the alerts on a T9 or T10 thermostat mean?
The T9 and the T10 and T10+ Pro have no code numbers. A red dot above the Menu icon shows there is an active alert, and you touch the message to read more. These are the alerts the two user guides list with a fault or a failure behind them:
| Alert on screen | Honeywell's meaning | Listed for |
|---|---|---|
| "HEAT PUMP FAILURE" | An issue was detected (L wire energized). Call a contractor to find what is wrong with the heat pump | T9, T10 |
| "MEMORY ERROR" | Failure of the memory chip. Replace the thermostat | T9, T10 |
| "INTERNAL SENSOR ERROR" | Failure of the sensor in the thermostat. Replace the thermostat | T9, T10 |
| "WIFI MODULE ERROR" | Failure of the Wi-Fi module. Replace the thermostat | T9, T10 |
| "INDOOR SENSOR ERROR" | An issue with the named wireless sensor. The sensor may need to be replaced | T9, T10 |
| "INDOOR SENSOR CONNECTION ERROR" | The named sensor is no longer connected. Replace its batteries and check where it is placed | T9, T10 |
| "OUTDOOR SENSOR ERROR" | The outdoor temperature sensor is no longer detected | T10 |
| "REDLINK RF TOOLKIT NOT RESPONDING" | The wireless sensor network is not operating. Contact Customer Care | T10 |
A "POWER RESTORED" alert on either model only tells you the power was interrupted and has come back. Honeywell's action for it is "No Action Required."
Do the T4 Pro and VisionPRO show error codes?
Not in their user documents. The T4 Pro user guide describes the same "ALRT" menu as the T6 Pro and a "REPL" (replace air filter) reminder, but it does not list numbered codes. The VisionPRO TH8000 operating manual has no error code table at all; its alerts are reminders for the filter, humidifier pad and UV lamp, which you cancel with the RESET key. If your thermostat shows a code that is not on this page, the guide for your exact model is the place to check.
What can you do from the thermostat?
Read the code, find your family above, and sort it into one of three groups:
- Reminders and setup alerts such as 171, 181, 182, 388 or "SET DATE AND TIME": handle these on the thermostat or in the app.
- Thermostat failures such as 170, 173 or "MEMORY ERROR": Honeywell's instruction is to replace the thermostat.
- Equipment and sensor faults such as 164, 177, 178 or "HEAT PUMP FAILURE": these point to the heat pump, a wired sensor or its wiring, and a licensed HVAC technician should handle them.
While you wait for service, make sure the mode and system type look right and give the system its compressor protection wait after any change, so you are not chasing a normal delay.
Is the code a filter, battery, date or Wi-Fi alert (171, 181, 182, 405, 407, 388, 399, 400, 607, E01, E02, E42, E43 or E99)?
- Yes
You can handle it on the thermostat or your network. Clear the reminder from the "ALRT" menu where your model allows it.
- No
Does Honeywell say to replace the thermostat (170, 173, MEMORY ERROR, INTERNAL SENSOR ERROR)?
- Yes
The thermostat itself has failed. Contact your installer or Honeywell Home about a replacement.
- No
The code points to the heat pump or a wired sensor. Leave the settings as they are and call a licensed HVAC technician.
- Yes
For other messages on these thermostats, see the Honeywell Home hub.
Frequently asked questions
- What does code 164 mean on a Honeywell thermostat?
- On the T6 Pro and the FocusPRO S200, 164 means the heat pump is signaling a fault to the thermostat through its L terminal. Honeywell describes it as the heat pump telling the thermostat there is a problem. It points to the equipment, so a licensed HVAC technician should handle it.
- Can I clear an error code on my Honeywell thermostat?
- Reminders, such as the filter reminders 181 and 182 on the T6 Pro, can be snoozed for 7 days or cleared from the "ALRT" menu. Honeywell says some alerts cannot be snoozed or cleared, and the FocusPRO S200 manual says its alerts cannot be dismissed at all. Those stay until the cause is fixed.
- What does E02 mean on a Honeywell Wi-Fi thermostat?
- On the FocusPRO TH6320WF1005 Wi-Fi Series, E02 means the Wi-Fi password was wrong. The code shows for 30 seconds and the thermostat goes back into Wi-Fi setup so you can enter the password again.
- Which Honeywell codes mean the thermostat itself has failed?
- On the T6 Pro, 170 (memory failure) and 173 (internal sensor failure) come with the instruction to replace the thermostat. The T9 and T10 guides give the same instruction for "MEMORY ERROR", "INTERNAL SENSOR ERROR" and "WIFI MODULE ERROR".