09 Low

Unical 09 Fault Code

The Unical 09 fault code means: your boiler has lost connection to the outdoor temperature sensor, meaning it may not adjust its heating automatically based on the weather outside.. It appears on 2 Unical models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: EXTERNAL PROBE interrupted. Check the wiring, if needed replace the external probe
Typical repair cost £90-150 (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 09 fault code

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

Source

Unical 09 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