High Lockout
F17 on Vaillant ecoMAX Pro 28E

Your boiler has detected that the electrical supply coming into the unit is currently too low for it to operate safely.

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

Power supply <170 V

What causes this 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 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

F10View →F11View →

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