BoilerFaultCodesViessmann CE Fault Code
The Viessmann CE fault code means: your boiler is having trouble 'talking' to an add-on device, such as an extra heating controller or an external sensor module.. It appears on 7 Viessmann models in our database.
Technical description: Communication error - ext. extension. Control mode
What causes the Viessmann CE fault?
This fault occurs when the boiler's main brain loses its connection with an external accessory, such as a specialist wiring centre or an extra heating zone controller. It is usually caused by a loose connection in the communication wiring or a circuit failure within the plug-in module itself, preventing the two devices from sharing data. In some cases, a power surge may have 'scrambled' the communication line, causing the boiler to lose track of the connected equipment.
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 CE fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann CE 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