F20 error; thermostat cannot detect presence or occupancy.

Safety first: No mains work is required.

Steps:

• 1. Check settings: In the thermostat menu or app, ensure occupancy-based control is enabled and configured correctly.
• 2. Clear obstructions: Make sure no objects, tape, or paint cover the sensor window on the thermostat.
• 3. Test detection: Stand in front of the thermostat and move within the specified range. Watch for any on-screen indicator of motion.
• 4. Reboot and update: Restart the thermostat and check for firmware updates.
• 5. Replace thermostat: If the sensor hardware has failed, the thermostat head will need replacement.