What are the alert codes and what do they mean?

The thermostat displays 3-digit alert codes when an issue is detected. For example, code 164 means the heat pump needs service, code 173 indicates a thermostat temperature sensor error, and code 399 means the internet connection has been lost. To view an active alert, touch Menu on the home screen, then touch Select to see the alert code and a scrolling description of the required action. (Pages 27–28)