How much does it cost to fix Ariston error code A12?

Typical repair cost for the Ariston A12 fault is £120-200 including labour.

A12 High

Ariston A12 Fault Code

Q: What does the Ariston A12 fault code mean?

Your boiler has detected that the internal water filter is blocked, which is preventing water from circulating properly to provide you with heating or hot water.

The Ariston A12 fault code means: your boiler has detected that the internal water filter is blocked, which is preventing water from circulating properly to provide you with heating or hot water.. It appears on 9 Ariston models in our database.

Technical description: Filter

Typical repair cost £120-200 (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 A12 fault code

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

Challenger 80E Repair: £120-200
Clas One Repair: £150-300
E-Combi One Repair: £120-200
E-Combi One 30 Repair: £120-200
Euro Combi 30 MFFI Repair: £90-180
Euro Prisma 24 Repair: £90-180
Genus 24 MFFI Repair: £120-250
Micro Combi 27 MFFI Repair: £120-250
Microsystem 15 Repair: £120-200

Source

Ariston A12 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