BoilerFaultCodesViessmann A2:2 Fault Code
Also written as A22 — same fault.
The Viessmann A2:2 fault code means: your boiler is likely experiencing a communication or pump error where it is struggling to switch between heating your house and heating your hot water tank.. It appears on 5 Viessmann models in our database.
Technical description: With DHW cylinder priority applicable to heating circuit pump and mixer
What causes the Viessmann A2:2 fault?
This fault occurs when the boiler's control system loses communication with the internal pump or can no longer control the distribution of heat between your radiators and hot water tank. The most common reason is a physical failure of the circulation pump or a loose wiring connection that prevents the main computer board from sending instructions. Even if the pump is spinning, the boiler may trigger this code if it isn't receiving the correct feedback signal from the motor.
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 A2:2 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann A2:2 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