BoilerFaultCodesVokera AF Fault Code
The Vokera AF fault code means: your boiler has detected very cold temperatures and has automatically turned itself on to prevent the internal pipes from freezing.. It appears on 3 Vokera models in our database.
Technical description: Frost protection system has been activated
What causes the Vokera AF fault?
This code appears when the boiler's internal temperature sensors detect that the water inside the unit has dropped to a level where it is at risk of freezing. To protect the heat exchanger and pipes from expanding ice damage, the boiler automatically fires up the burner to warm the water back to a safe temperature. Once the system reaches a secure temperature, the code will clear and the boiler will return to normal operation.
This display is almost exclusively seen during the winter months or during sudden overnight cold snaps when temperatures drop near freezing.
DIY fix possible
Check that your gas and electricity supplies are still activeEnsure any exposed external pipework (condensate pipe) is insulated or not frozenMonitor the boiler; the code should disappear once the water temperature inside the unit rises sufficiently
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Gas Safe Register →Vokera models that show the AF fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vokera AF fault code information on this page is sourced and cross-checked against the official Vokera service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026