12 High

Unical 12 Fault Code

The Unical 12 fault code means: your boiler has stopped working because it cannot correctly detect the temperature of the water being used for your heating system.. It appears on 2 Unical models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: HEATING SENSOR (11) Heating sensor fault (Par.4) or its connections.
Typical repair cost £120-220 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Unical models that show the 12 fault code

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

Source

Unical 12 fault code information on this page is sourced and cross-checked against the official Unical service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026