25 High

Unical 25 Fault Code

The Unical 25 fault code means: your boiler's electronic control system has lost its tuning settings and cannot properly regulate the gas and air mixture for combustion.. 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: No Calibration. GAC Calibration 4.3.1
Typical repair cost £100-250 (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 25 fault code

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

Source

Unical 25 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