DIAGNOSIS: The display brightness setting is on its lowest level or the ambient light sensor is obstructed.
FIX: Adjust the brightness manually. Press Menu > Settings > Preferences > Display Brightness. Choose Medium or High. The setting is not auto-saved; press Back to exit and save.
IF THAT DIDN'T WORK: Check for a protective film or case covering the light sensor, located at the top center of the thermostat faceplate. Remove any obstruction. The sensor automatically adjusts brightness based on room light.
HEADS UP: A persistently dim screen, even on the highest manual setting, can indicate impending display failure or a low-voltage issue with the C-wire. Monitor if the problem worsens over time.