HL High

Unical HL Fault Code

The Unical HL fault code means: your boiler has overheated, causing a safety sensor to automatically shut the system down to prevent damage.. 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: Safety thermostat
Typical repair cost £120-280 (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 HL fault code

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

Source

Unical HL 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