Thermostat plastic housing feels unusually warm to the touch during normal operation.

Safety first: Turn off HVAC power at the breaker before removing the thermostat from the wall plate.

• Step 1 – Check location and wall cavity: Ensure the thermostat is not above a heat source. Seal any large wall openings behind the wall plate to prevent warm air from rising behind the unit.
• Step 2 – Clear vents: Make sure the thermostat's vents are not blocked by paint, wallpaper, or obstructions. Clean dust with a soft brush.
• Step 3 – Measure voltage: Confirm that 24 VAC between R and C is within normal range; significantly low voltage can cause the internal regulator to run hotter.
• Step 4 – Monitor for errors: If no over‑temperature errors (like E15) appear and the thermostat is only mildly warm, this may be normal. If it is hot to the touch or errors appear, replace the thermostat.