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 27 April 2026

Fault code Mains ON Only appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has stopped working and is showing a fault light, meaning it has detected an internal error that has forced it to shut down for safety. (As reported on Potterton Puma 80/100)

Pick your boiler brand for the Mains ON Only fix

Potterton Mains ON Only 5 models

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 27 April 2026