BoilerFaultCodesAriston 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 7 Ariston models in our database.
Technical description: Check of domestic hot water production efficiency (delivery rate and temperature)
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.
- Ariston Challenger 80E manual (PDF)
- Ariston E-Combi One 30 manual (PDF)
- Ariston Eurocombi A/23 MFFI manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026