Viessmann D6 Error [extra Quality] Now

On systems using Vitotronic 200 controls, D6 specifically points to a flow switch issue, indicating that the minimum required flow rate has not been reached.

Loose or corroded cables between the fan and the main control board (PCB) can disrupt signals. viessmann d6 error

If the fan and flow switch are working correctly, the control board itself may be misinterpreting data. Troubleshooting and Solutions On systems using Vitotronic 200 controls, D6 specifically

Dust, debris, or a mechanical fault can prevent the fan from reaching the required RPMs. On systems using Vitotronic 200 controls

The precise definition of a D6 error varies slightly across the Viessmann product range: