Viessmann D6 Error [2021] Jun 2026

The sensor itself can fail. It might be mechanically stuck due to debris, or its electrical contacts may have failed, sending a false "no flow" signal to the control board even when flow is present.

Have you fixed a D6 error on your Viessmann? Share your experience in the comments below. viessmann d6 error

In plain English: Your boiler’s brain is trying to send signals to the body (the burner, pump, valves), but no one is answering. As a safety measure, the boiler enters a (hard lockout) to prevent unsafe operation. You will likely see a red fault light and the boiler will stop heating water or radiators. The sensor itself can fail