BoilerFaultCodesViessmann 05 Fault Code
The Viessmann 05 fault code means: your boiler has detected a sequence of ignition or flame detection errors and has shut itself down for safety.. It appears on 7 Viessmann models in our database.
Technical description: Burner control switches to lockout
What causes the Viessmann 05 fault?
This fault occurs when the boiler's internal computer fails to detect a reliable flame during the ignition process. The most common reasons are worn-out sparks that can no longer light the gas, or a dirty sensor that cannot 'see' the flame even after it has started. It can also be caused by a lack of gas reaching the burner due to a faulty valve or a blockage in the air supply.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the 05 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 05 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026