High Mains Voltage High

Keston High Mains Voltage Fault Code

Also written as HIGHMAINSVOLTAGE — same fault.

The Keston High Mains Voltage fault code means: your boiler has detected that the electricity coming from your home's mains supply is higher than it is designed to handle, which is causing it to shut down to prevent internal electrical damage.. It appears on 2 Keston models in our database.

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: Voltage exceeds operational requirements
Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Keston models that show the High Mains Voltage fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Keston High Mains Voltage fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026