Vaillant smart thermostat shows F.11 and the time/date keep resetting or drifting significantly.

Safety: No mains work required.

• 1. Enable internet sync: Ensure the thermostat or gateway is connected to the internet and NTP/time sync is enabled in settings.
• 2. Correct time zone: In the Vaillant app or thermostat menu, set the correct country, region, and time zone, and enable automatic daylight saving adjustments.
• 3. Manual time set: If internet is unavailable, set the time and date manually and monitor for drift over 24–48 hours.
• 4. Firmware update: Check for and install any firmware updates that may address clock issues.
• 5. Replace thermostat: If the clock drifts excessively or resets even with correct settings and updates, the internal RTC backup may be defective; replace the thermostat.