BoilerFaultCodesViessmann 81:0 Fault Code
Also written as 810 — same fault.
The Viessmann 81:0 fault code means: your boiler has been manually switched between heating and hot water modes, and it is simply notifying you that a changeover has occurred.. It appears on 5 Viessmann models in our database.
Technical description: Manual summer/winter changeover
What causes the Viessmann 81:0 fault?
This code appears when the boiler's control settings have been intentionally adjusted to turn off the central heating while keeping the hot water active. It is triggered by a manual user selection on the control panel, often done to save energy when heating isn't needed. There is no mechanical failure; the boiler is simply following a command to operate in 'hot water only' mode.
This code is most frequently seen during the spring and summer months when homeowners manually switch over to summer mode.
DIY fix possible
Check the control panel to see if Summer or Winter mode was selected recentlyNavigate the menu to 'Heating and Hot Water' settingsAdjust the date and time settings to ensure the automatic changeover works correctly in the future
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Gas Safe Register →Viessmann models that show the 81:0 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 81:0 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