BoilerFaultCodesViessmann 71:2 Fault Code
Also written as 712 — same fault.
The Viessmann 71:2 fault code means: your boiler is having trouble heating your hot water cylinder because a sensor has detected an unusually high temperature or a fault during the heating process.. It appears on 5 Viessmann models in our database.
Technical description: ON during DHW loading to set value 1
What causes the Viessmann 71:2 fault?
This fault occurs when the temperature sensor in your hot water cylinder detects a reading that is significantly higher than expected or rises too rapidly. This is often caused by a faulty sensor sending incorrect data to the boiler, or a mechanical failure like a stuck diverter valve preventing heat from moving correctly to your water tank. In some cases, it can also indicate a blockage in the heat exchanger that is causing the system to overheat locally.
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 71:2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 71:2 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