BoilerFaultCodesViessmann 65:2 Fault Code
Also written as 652 — same fault.
The Viessmann 65:2 fault code means: your boiler is having trouble directing water to your radiators or taps because an internal motor has likely become stuck or failed.. It appears on 5 Viessmann models in our database.
Technical description: Diverter valve by Wilo
What causes the Viessmann 65:2 fault?
This fault occurs when the internal moving parts of the diverter valve become stuck or the motor that drives them fails to reach the correct position. This is often caused by a buildup of debris or sludge from the heating system water creating friction, which prevents the valve from switching between your heating and hot water.
This fault is more frequent in autumn when the heating is turned on for the first time after summer, as the valve may have seized during the long period of inactivity.
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 65:2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 65:2 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