4 12 Medium

Ariston 4 12 Fault Code

Also written as 412 — same fault.

The Ariston 4 12 fault code means: your boiler is having trouble communicating with the temperature sensor for your secondary heating zone, meaning it doesn't know how warm that specific part of your home is.. 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: Room sensor circuit open or short circuit ZONA 2

What causes the Ariston 4 12 fault?

This fault occurs when the boiler's control board can no longer read temperature data from the thermostat or sensor dedicated to the second heating area of your home. The most common reason is a loose electrical connection, a broken wire, or a failure within the sensor itself that prevents it from sending a signal.

Typical repair cost £120-250 (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 4 12 fault code

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

Source

Ariston 4 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