Honeywell Thermostat Error Codes: 171, E02 and E1 33

For 171, set the date as well as the time

Resideo lists 171 as a request for the date and time so features such as the schedule can operate. For a T6 Pro Smart that is not connected to WiFi, its guide gives these steps:

1. Touch Menu, use the arrows to find CLOCK, then touch Select.
2. Find SET TIME and touch Select. Adjust the time with the plus or minus button and touch Done.
3. Return to Menu, find DATE and touch Select.
4. Set the month and confirm with Select. Set the day and year the same way, using Select to save.

Resideo says a T6 Pro Smart connected to WiFi and registered to the Resideo App sets its date and time automatically. On that setup, CLOCK and DATE are absent from the menu. If yours is connected and registered but still shows 171, give support that detail rather than hunting for a missing button.

Separate a service alert from a maintenance reminder

For the two T6 Pro Smart models above, Resideo’s alert table makes these distinctions:

Resideo says some critical alerts cannot be dismissed or snoozed. A missing Dismiss button is not a reason to erase the thermostat setup.

Have the return air sensor circuit checked

For a FocusPRO wireless thermostat used with an equipment interface module, Resideo’s code 33 instruction is to check the return air sensor wiring. In Resideo’s layout, the module, called the EIM, sits near or on the heating and cooling equipment.

Resideo gives a procedure to clear E1 33 if the return air sensor is being removed permanently. It then directs the installer to reconnect the wireless devices. That is a system change, not an everyday way to clear a warning.

Resideo describes this optional sensor as backup control if thermostat power is lost. For hydronic heating, its guide instead specifies a remote indoor sensor in the living space. Keep the sensor in place and give the installer the full code.

Other codes in the same FocusPRO installation guide point elsewhere:

• 29: the wireless devices being connected are incompatible.
• 30: an invalid zone number; this EIM setup requires zero.
• 34: low wireless signal strength.
• 38: the installer must check that the EIM’s Connected light is flashing and that they are at least two feet away from the EIM.
• 53: the thermostat is not receiving outdoor temperature and humidity information.

For 53, Resideo lists either a configuration needing an outdoor sensor that has not been connected, or a sensor that may no longer be communicating. Have the installer distinguish those cases before changing equipment settings.

Use the network fix for the code you have

On the RTH6500WF models named above, Resideo gives this list. These meanings belong to that series, even if another Honeywell thermostat shows similar characters.

For E42 after that wait, or E99, Resideo specifies removing the thermostat from its wall plate for ten seconds, then reconnecting it. Keep the wall plate and its wires attached. This is the restart given for those RTH6500WF codes, not a reset recipe for every Honeywell model.

For a T6 Pro Smart instead, Resideo calls 399 lost internet and 400 lost WiFi signal. For 399, check network settings; for 400, wait for reconnection or select a new WiFi network. These are separate from its 168 radio fault in the earlier table.

Check what the heating or cooling is doing

Resideo says the RTH6500WF can operate heating and cooling with or without WiFi. If its network code clears but the house still gets no heat, move to the thermostat and equipment checks rather than repeating network setup.

For a service visit, pass on whether the code began after installation, a router change or a power loss. Include the model and message you recorded at the start. That gives the technician a clear starting point without changing the system before they arrive.

If you are considering erasing settings, the guide to thermostat restarts and resets explains the different choices.