Viessmann D6 Error May 2026

A stuck pump, airlock, or blocked filter can cause the flow switch to trigger a D6 error because water isn't moving through the heat exchanger fast enough.

If the fan and flow switch are working correctly, the control board itself may be misinterpreting data. Troubleshooting and Solutions viessmann d6 error

Dust, debris, or a mechanical fault can prevent the fan from reaching the required RPMs. A stuck pump, airlock, or blocked filter can

In some configurations, it may indicate a fault at the DE1 connection on the external safety device adapter. Common Causes of a D6 Fault Several underlying issues can trigger this lockout: A stuck pump