Thermostat shows much higher or lower room temperature than actual, but no sensor error code is displayed.

Safety note: Only minimal work is needed; avoid opening mains compartments.

Steps to correct:

• 1. Compare with reliable thermometer: Place a calibrated thermometer near the thermostat and compare readings over 15–20 minutes.
• 2. Seal cable entry: If cold air is entering through the cable hole behind the thermostat, seal it with non-flammable filler or foam (power off first).
• 3. Adjust offset: Use the thermostat’s temperature offset or calibration setting to correct the displayed temperature.
• 4. Relocate if necessary: If the wall is significantly warmer/colder than the room, consider relocating the thermostat to a more representative location.

When to call a professional: If the reading is unstable or varies wildly, the sensor may be failing and the thermostat should be replaced.