High Lockout
F.17 on Vaillant ecoMAX Pro 28E

Your boiler has detected that the electrical wiring is connected incorrectly or there is a problem with the mains power supply.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Check the polarity of your system.

What causes this 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 is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F.13View →F.27View →F.63View →

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