16 High

Unical 16 Fault Code

The Unical 16 fault code means: your boiler has temporarily locked out because the internal temperature has dropped dangerously close to freezing, which risks damaging the heat exchanger.. 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: EXCHANGER FREEZING ( 24 ) Exchanger freezing is detected If the heating sensor detects a temperature below 2° C, burner ignition is inhibited until the sensor detects a temperature above 5°C. Disconnect the from the power supply, close the gas valve, defrost the exchanger carefully.
Typical repair cost £90-180 (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 16 fault code

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

Source

Unical 16 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 31 August 2026