Viessmann D6 Error [UPDATED]

: Check the external flue terminal for any visible blockages or damage.

The "DE1" input on the boiler is reporting a fault. This input is often used for external control devices, such as a pressure switch or an external safety interlock. Viessmann Direct 💡 Quick Fixes to Try viessmann d6 error

Unlike a standard "Lockout" error (e.g., F2 or F4), D6 is often an informative fault Identify the External Device: Check which piece of equipment is connected to the EA1 module's DE1 input : Check the external flue terminal for any