BoilerFaultCodesVaillant F16 Fault Code
The Vaillant F16 fault code means: your boiler thinks it still sees a flame even though it has commanded the burner to turn off, which is a safety concern that prevents it from restarting.. It appears on 2 Vaillant models in our database.
Technical description: Flame detection fault (flame presence >5 s after burner stop)
What causes the Vaillant F16 fault?
This fault occurs when the boiler’s safety sensors continue to detect a flame for more than five seconds after the gas supply should have been cut off. The most common reason is that the gas valve hasn't closed fully or the electrode that monitors the flame has become damaged and is sending a false signal. Because this is a major safety concern, the boiler will automatically shut itself down to prevent any risk.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Vaillant models that show the F16 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F16 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 27 April 2026