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

Typical repair cost for the boiler ON ON FLASH fault is £280-450 including labour.

ON ON FLASH High

Boiler Fault Code ON ON FLASH

Also written as ONONFLASH — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code ON ON FLASH appears across 2 boiler brands and 28 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's internal computer has developed a fault and can no longer control the heating process safely. (As reported on Baxi Solo)

Pick your boiler brand for the ON ON FLASH fix

Baxi ON ON FLASH 24 models Potterton ON ON FLASH 4 models

Source

Information for the ON ON FLASH 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