A 39 High

Ariston A 39 Fault Code

Also written as A39 — same fault.

The Ariston A 39 fault code means: your boiler's main internal computer has detected a critical electronic error that is preventing it from functioning correctly.. It appears on 2 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: MCU fault 1
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 A 39 fault code

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

Source

Ariston A 39 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 31 August 2026