How much does it cost to fix boiler error code Slow flash?

Typical repair cost for the boiler Slow flash fault is £120-250 including labour.

Slow flash High

Boiler Fault Code Slow flash

Also written as SLOWFLASH — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code Slow flash appears across 2 boiler brands and 4 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 a safety concern or internal fault and has automatically shut down to protect itself, requiring you to attempt a manual reset. (As reported on Worcester Bosch 28Si)

Pick your boiler brand for the Slow flash fix

Grant Slow flash 1 model Worcester Bosch Slow flash 3 models

Source

Information for the Slow 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 31 August 2026