Thermostat backlight or display is very dim and hard to read, even though the unit otherwise works.

Safety first: No high-voltage work is required for brightness settings; turn off power before checking wiring.

Steps to troubleshoot:

• 1. Adjust brightness: In the thermostat display settings, increase brightness and backlight timeout.
• 2. Check voltage (technician): Have a technician verify 24V between R and C at the thermostat. Low voltage can dim the display.
• 3. Replace thermostat: If brightness is maxed and voltage is normal but the display remains dim, the backlight is failing and the thermostat should be replaced.