Your Lyric thermostat is equipped with low-power features. If it does not have AC power through its C wire, it will draw power from your heating and cooling systems to continue operating. Because this does not provide as much power, the Lyric's screen goes to sleep when not being used to conserve energy. This does not affect its operation; it will continue to control your heating and cooling systems to maintain your preferred temperature, and its settings can be changed at any time from the Lyric app. In addition, it has a proximity sensor and will wake up again as you approach so you can make changes to its settings directly. If the thermostat does not wake up when you approach, please replace the AAA Lithium battery. Gently pull the thermostat away from the wallplate, remove the battery and replace it with a new one. To tell if your Lyric has AC power, gently pull the thermostat away from the wallplate and look at your wiring. If you have a wire in the C terminal, you should have AC power and your Lyric's screen should not go blank. Confirm that your wiring is correct.