BoilerFaultCodesVaillant F.17 Fault Code
Also written as F17 — same fault.
The Vaillant F.17 fault code means: your boiler has detected that the electrical wiring is connected incorrectly or there is a problem with the mains power supply.. It appears on 4 Vaillant models in our database.
Technical description: Check the polarity of your system.
What causes the Vaillant F.17 fault?
This fault occurs when the boiler detects that the live and neutral electrical wires have been swapped, or there is an issue with the earth connection. It is most commonly caused by recent electrical work in the home or an incorrectly wired fused spur switch that provides power to the unit. In some cases, a failing internal circuit board can also misread the electrical signals and trigger this safety shutdown.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Vaillant models that show the F.17 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Vaillant F.17 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