BoilerFaultCodesVaillant F17 Fault Code
The Vaillant F17 fault code means: your boiler has detected that the electrical supply coming into the unit is currently too low for it to operate safely.. It appears on 2 Vaillant models in our database.
Technical description: Power supply <170 V
What causes the Vaillant F17 fault?
This fault occurs when the electrical voltage entering the boiler drops below a safe threshold, meaning there is not enough power for the internal components to function. Typically, this is caused by a problem with your home's main electricity supply or a failing electronic control board within the boiler itself. In some cases, it can also be triggered by a loose or damaged power cable that is preventing a steady flow of electricity.
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 F17 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F17 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