AA9999 High

Ariston AA9999 Fault Code

The Ariston AA9999 fault code means: your boiler's computer is experiencing an internal error and cannot properly check or control the system, meaning it needs an expert to reset or replace the main control unit.. It appears on 3 Ariston models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Problem with the electronic monitoring
Typical repair cost £250-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Ariston models that show the AA9999 fault code

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

Source

Ariston AA9999 fault code information on this page is sourced and cross-checked against the official Ariston service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026