BoilerFaultCodesViessmann 97:2 Fault Code
Also written as 972 — same fault.
The Viessmann 97:2 fault code means: your boiler is having difficulty communicating with part of your heating control system, but it will continue to work using its own internal information.. It appears on 5 Viessmann models in our database.
Technical description: The outside temperature of the sensor connected to the control unit will be utilised internally and transmitted via LON BUS to any connected Vitotronic 050.
What causes the Viessmann 97:2 fault?
This fault occurs when the boiler's main control board loses the data connection from the outdoor weather sensor. The most common cause is a loose connection or a break in the wiring between the boiler and the sensor, though it can also be caused by a software glitch in the communication module. Because the boiler can no longer see the outside temperature, it will stop modulating based on the weather and revert to a basic backup setting.
This fault often becomes noticeable during the autumn or spring when fluctuating outdoor temperatures cause the expansion and contraction of the sensor's delicate electrical components.
DIY fix possible
Check for any visible damage to wiring leading to the outdoor sensorSwitch the boiler off and back on at the fused spur to refresh the connectionIf you have a Vitotronic 050 controller, check that it is powered on
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Viessmann models that show the 97:2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 97:2 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