Diagnosis
The internal temperature sensor is being influenced by a local heat source or is faulty.
How to Fix It
Relocate the thermostat. It must be on an interior wall, away from direct sunlight, drafts, doorways, and heat-generating electronics. Do not install it near a TV, lamp, or above a heat register. The sensor needs passive air to read accurately.
If That Didn't Work
Check for calibration. Go to Menu > Settings > Temperature Offset. You can adjust the reading +/- 5 degrees to match a known good thermometer. Place a accurate thermometer next to the thermostat for 2 hours to compare.
Heads Up
The thermostat generates a small amount of its own heat. This is normal. If it's mounted on an exterior wall without proper insulation, cold drafts behind the wall can skew the reading. Use the wall plate seals provided.