F3 Low

Alpha F3 Fault Code

The Alpha F3 fault code means: your boiler has automatically activated its internal heater to protect itself from freezing during cold weather.. It appears on 4 Alpha 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: Anti-freeze mode in progress. Boiler operating to restore the minimum safety temperature against boiler freezing.

Engineer required

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

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Alpha models that show the F3 fault code

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

Source

Alpha F3 fault code information on this page is sourced and cross-checked against the official Alpha service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026