Thermostat shows incorrect room temperature compared to actual conditions; system short cycles or runs too long.

Safety first: No high-voltage work is required.

Steps to troubleshoot:

• 1. Check location: Ensure the thermostat is away from direct sunlight, supply registers, exterior doors, and appliances that emit heat.
• 2. Seal wall opening: Remove the thermostat and seal the wall opening behind it with foam or putty to block drafts.
• 3. Adjust calibration: In the thermostat settings, adjust the temperature offset to match a reliable reference thermometer placed nearby.
• 4. Replace thermostat if needed: If large offsets are required or readings are unstable, the internal sensor may be failing and the thermostat should be replaced.