BoilerFaultCodesVaillant F.105 Fault Code
Also written as F105 — same fault.
The Vaillant F.105 fault code means: your boiler's computer has lost the specific internal calibration settings required to mix the gas and air correctly, meaning it cannot safely start up.. It appears on 3 Vaillant models in our database.
Technical description: Gas valve assembly offset incorrectly stored. If the gas valve or the PCB and the unit interface are replaced, the gas valve offset must be set.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Vaillant models that show the F.105 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.105 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026