Medium Warning
A0:2 on Viessmann Vitodens 333-F

Your boiler is having trouble communicating with the wall-mounted room controller and may need a simple reset to re-establish the connection.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

With Vitotrol 300 (automatic recognition)

What causes this fault?

This fault occurs when the boiler loses its digital handshake with the Vitotrol room controller, meaning they can no longer exchange temperature data. The most common reason is a temporary glitch in the communication bus or a loose connection in the low-voltage wiring between the two units. In some cases, it can also be caused by electrical interference or a failing internal communication module.

DIY fix possible

Check that the Vitotrol unit is securely clicked into its wall docking stationSwitch the boiler power off at the main isolation switch for 30 seconds, then back onEnsure the wiring to the wall controller has not been accidentally damaged or disconnected

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