12 Medium

Ariston 12 Fault Code

The Ariston 12 fault code means: your boiler is struggling to reach the correct temperature for your hot water, likely due to a build-up of limescale or a faulty internal sensor.. It appears on 6 Ariston 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: Check of domestic hot water production efficiency (delivery rate and temperature)
Typical repair cost £120-£280 (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 12 fault code

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

Source

Ariston 12 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