Your boiler's internal clock has lost its time setting, which is usually a minor issue that doesn't stop your heating or hot water from working.

DIY fix possible

Check the display on the boiler's control panel to confirm the current time and date are wrong or flashing.Use the control dial and buttons to set the correct time and date manually, following the 'Time and date' section in your Vitodens user manual.If your boiler is connected to the internet via a Viessmann gateway or the ViCare app, check that the Wi-Fi or internet connection is working, then allow up to 24 hours for the time to sync automatically.If the fault returns or the clock keeps losing time, contact a Viessmann-registered heating engineer, as the control unit's clock backup may need replacing.