How much does it cost to fix boiler error code High Mains Voltage?

Typical repair cost for the boiler High Mains Voltage fault is £120-250 including labour.

High Mains Voltage High

Boiler Fault Code High Mains Voltage

Also written as HIGHMAINSVOLTAGE — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code High Mains Voltage appears across 1 boiler brand and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning 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. (As reported on Keston C30 / C35)

Pick your boiler brand for the High Mains Voltage fix

Keston High Mains Voltage 2 models

Source

Information for the High Mains Voltage fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

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