How to Fix / Troubleshooting

Safety first: No hazardous work is required.

Check for firmware updates: Use the Viessmann app to update the thermostat firmware to the latest version.
Avoid rapid power cycling: Do not repeatedly switch power on and off; allow the device to shut down gracefully when possible.
Re‑enter time and schedules: After a power cut, re‑enter time and schedules and monitor whether they are retained on subsequent short outages.
Replace thermostat: If settings are consistently lost, the internal memory or backup power is defective and the thermostat should be replaced.

The thermostat loses all settings (time, schedules) after a power cut.

Possible Causes