Sometimes the D6 error is a temporary logic lock-up.
The D6 code indicates an . Your boiler’s electronic control unit sends power to the igniter, opens the gas valve, but does not receive a signal from the flame sensor that a fire is present. viessmann d6 error
If a reset doesn't work, an engineer will need to dive into the service menu Sometimes the D6 error is a temporary logic lock-up
Look inside the control housing:
An external device like a low water cut-off or a flow switch has triggered a shutdown. opens the gas valve
Verify the coding addresses in the Vitotronic logic to ensure the DE1 input is configured correctly for your specific setup.