DIAGNOSIS Oil and dust buildup on the capacitive glass screen and the stainless steel ring, interfering with touch and rotation sensitivity.
FIX Power off your HVAC system at the breaker. Pull the Nest display off the base. Use a dry, soft microfiber cloth to wipe the screen and ring firmly. For stubborn smudges, slightly dampen a corner of the cloth with distilled water. Never spray liquid directly onto the thermostat.
IF THAT DIDN'T WORK The ring mechanism may have physical debris inside. While the display is off, rotate the ring fully several times to dislodge any particles. Inspect the gap between the ring and the body for visible obstructions.
HEADS UP Never use cleaning sprays, solvents, window cleaners, or compressed air. These can damage the screen coating and force moisture into the electronics. The display is not sealed against liquid intrusion.