How much does it cost to fix boiler error code Mains ON Only?

Typical repair cost for the boiler Mains ON Only fault is £150-300 including labour.

Mains ON Only High

Boiler Fault Code Mains ON Only

Also written as MAINSONONLY — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code Mains ON Only appears across 1 boiler brand and 1 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 an internal fault that has caused it to stop heating your home and hot water for safety reasons. (As reported on Potterton Prima 30B)

Pick your boiler brand for the Mains ON Only fix

Potterton Mains ON Only 1 model

Source

Information for the Mains ON Only 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