While some initial checks can be performed by a homeowner, most D6 repairs require a Gas Safe registered engineer due to the involvement of the gas burner and internal electrical components. Viessmann Fault Code Checker
Contact a professional engineer to test the electrical switch and clean out system debris. viessmann d6 error
Before the error code appears, you might notice one or more of these symptoms: While some initial checks can be performed by
Use a radiator key to open the valve slightly (counter-clockwise). Allow water (not just air) to escape into a container. Allow water (not just air) to escape into a container
Is the error or does it happen every single time you try to turn it on?
The indicates a serious safety issue: the maximum temperature limiter (STB) has tripped , or there is an active flue gas temperature fault . When this error occurs, your boiler will immediately shut down and enter a lockout state to prevent severe overheating and potential component damage.