Check the setting of your heating system:
- Is it still set to summer mode?
- Does the heating run exclusively on DHW heating?
- Is the system time set correctly?
- Has the system jumped back to the default setting after a power cut?
These settings can be read directly from the display of your Viessmann heating system. With most Viessmann systems, they can be changed via a mechanical controller or via the display's touchscreen. For older heating systems, it is highly recommended to call in an installer to avoid causing damage with the incorrect settings.