Error 120; thermostat reports that the humidity sensor is faulty or readings are out of range.

Safety: Turn off power before opening the thermostat casing.

• Visual inspection: Check for signs of moisture, corrosion, or dust buildup around the sensor area (often a small vented section).
• Drying: If recently exposed to high humidity or splashes, allow the thermostat to dry in a warm, dry room (power off) for several hours.
• Clean gently: Use dry compressed air to blow away dust; do not use liquids directly on the sensor.
• Disable humidity control: If humidity-based functions are not critical, disable them in settings to clear alarms.
• Replace thermostat: If humidity readings remain unrealistic, the sensor is likely defective and not user-replaceable.