A99 High

Ariston A99 Fault Code

The Ariston A99 fault code means: your boiler's internal computer has encountered a communication error or software glitch that is preventing it from monitoring the system's safety and operation.. It appears on 7 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-£550 (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 A99 fault code

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

Source

Ariston A99 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 27 April 2026