BoilerFaultCodesViessmann A2 Fault Code
The Viessmann A2 fault code means: your boiler has sensed that the internal pump is malfunctioning or water is not circulating correctly, which has caused the system to stop as a safety precaution.. It appears on 8 Viessmann models in our database.
Technical description: N/A
What causes the Viessmann A2 fault?
This fault occurs when the boiler's internal sensors detect that water is not moving through the heat exchanger as quickly or efficiently as it should. The most common reason is a mechanical failure of the circulation pump or a buildup of debris that has physically jammed the pump's internal components. In some cases, it may also be triggered by a communication error where the main control board is unable to tell the pump to spin.
This fault is more frequent in autumn when the heating is turned back on after a long summer break, as pumps can often seize up during months of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Viessmann models that show the A2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann A2 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 050-W manual (PDF)
- Viessmann Vitodens 111-W manual (PDF)
- Viessmann Vitodens 200-W manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026