Thermostat shows room temperature that is clearly inaccurate (too high or too low)

Safety first: Only low-voltage work is involved; no high-voltage exposure.

• Step 1 – Compare with reference: Place an accurate thermometer near the thermostat and compare readings after 15–20 minutes.
• Step 2 – Check location: Ensure the thermostat is not in direct sunlight, above supply registers, near exterior doors, or on an uninsulated exterior wall. If it is, consider relocating the thermostat.
• Step 3 – Seal wall opening: Remove the thermostat and seal the wall opening behind it with foam or putty to prevent drafts from affecting the sensor.
• Step 4 – Adjust calibration: Use the thermostat’s temperature offset or calibration setting to correct minor differences (typically ±3°F).
• Step 5 – Replace thermostat: If the reading is off by a large amount and does not respond to calibration, the internal sensor may be defective and the thermostat should be replaced.

When to call a professional: For relocation or new wiring runs, contact an HVAC technician or electrician.