9A Low

Viessmann 9A Fault Code

The Viessmann 9A fault code means: your boiler has lost communication with the solar panel sensor on your roof, meaning it can no longer monitor the solar heating system properly.. It appears on 2 Viessmann models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Lead break, collector temperature sensor (solar control module)
Typical repair cost £140-£240 (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 9A fault code

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

Source

Viessmann 9A 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 7 July 2026