A0:1 Medium

Viessmann A0:1 Fault Code

Also written as A01 — same fault.

The Viessmann A0:1 fault code means: your boiler has lost communication with its remote control unit, meaning it may not be receiving the correct instructions to heat your home.. It appears on 5 Viessmann models in our database.

Book a service

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 200 (automatic recognition)

What causes the Viessmann A0:1 fault?

This fault occurs when the link between your boiler and its wall-mounted control unit is broken. The most common reasons are a loose wiring connection at either end, damage to the communication cable, or a internal glitch in the control unit's electronic circuit board.

Typical repair cost £90-250 (including labour)

DIY fix possible

Check the thermostat or remote control unit is properly docked/mountedInspect the wiring between the boiler and the wall controller for any obvious loose connectionsTurn the boiler power off and back on to trigger a re-recognition of the remote unit

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Viessmann models that show the A0:1 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann A0:1 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