A5:0 Medium

Viessmann A5:0 Fault Code

Also written as A50 — same fault.

The Viessmann A5:0 fault code means: your boiler has detected that the water pump responsible for circulating heat to your radiators is not behaving as expected, which may result in your heating not working correctly.. 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: Without heating circuit pump logic function
Typical repair cost £180-350 (including labour)

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 A5:0 fault code

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

Source

Viessmann A5:0 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