Thermostat shows A7 and the time or date cannot be synchronized; schedules may run at incorrect times.

Safety first: No electrical work is required.

• Check network and cloud connection: Ensure the thermostat is online and connected to the Viessmann cloud (no A5 error).
• Verify time zone: In the Viessmann app or thermostat menu, confirm that the correct time zone and daylight saving settings are selected.
• Manual time set: If automatic sync fails, set the time and date manually on the thermostat and save the settings.
• Firmware update: Check for and install any available firmware updates that may address time sync issues.
• If clock drifts quickly: Persistent drift indicates an internal clock fault; replacement of the thermostat may be required.