Room temperature reading on thermostat is significantly inaccurate compared to a reliable thermometer

Safety: No high-voltage work is required; HVAC power can remain on.

• Check location: Ensure the thermostat is not near windows, doors, lamps, electronics, or supply vents.
• Seal wall opening: Remove the thermostat and use foam or putty to seal the hole in the wall behind the wall plate to prevent drafts from affecting the sensor.
• Compare readings: Place a known-accurate thermometer near the thermostat and compare after 30 minutes. A small difference (1–2°F) is normal.

If the reading remains off by more than ~3°F after addressing drafts and location, the internal sensor may be failing and the thermostat should be replaced.