BoilerFaultCodesAriston 12 Fault Code
The Ariston 12 fault code means: your boiler is struggling to heat your tap water effectively, meaning it may not reach the desired temperature or the flow is too weak.. It appears on 5 Ariston models in our database.
Technical description: Check of domestic hot water production efficiency (delivery rate and temperature)
DIY fix possible
Check that the cold water mains stopcock is fully openInspect all hot water taps for limescale buildup and clean the aeratorsEnsure the temperature control dial on the front of the boiler is set correctly
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like 12: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
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 31 August 2026