BoilerFaultCodesViessmann 97:1 Fault Code
Also written as 971 — same fault.
The Viessmann 97:1 fault code means: your boiler is receiving the outdoor weather information from another connected device on your home network rather than its own direct sensor.. It appears on 5 Viessmann models in our database.
Technical description: Outside temperature is adopted by the LON BUS
What causes the Viessmann 97:1 fault?
This occurs because your boiler has detected that it is receiving outdoor temperature data from another device on your home network rather than from its own dedicated sensor. It typically happens when the boiler is linked to a wider building management system or a smart home network that takes over the job of telling the boiler how cold it is outside. This isn't a mechanical breakdown, but rather a change in how the boiler's computer is communicating with other parts of your home.
DIY fix possible
Check if any other connected heating controls or smart home devices have been recently updated or restartedPress the 'Reset' button on the boiler control panelMonitor the boiler display; if your heating is working normally, no further action is required
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the 97:1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 97:1 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