BoilerFaultCodesViessmann 71:1 Fault Code
Also written as 711 — same fault.
The Viessmann 71:1 fault code means: your boiler is struggling to heat your hot water tank because it is reaching its internal safety temperature limit before the tank is actually full.. It appears on 5 Viessmann models in our database.
Technical description: OFF during DHW loading to set value 1
What causes the Viessmann 71:1 fault?
This fault occurs when the boiler is unable to transfer heat to your hot water tank quickly enough, causing the internal water temperature to climb too high and trigger a safety shutdown. The most common reasons are a faulty sensor giving the boiler incorrect readings or a mechanical failure in the valve that directs hot water to your cylinder.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 71:1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 71:1 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