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

Typical repair cost for the boiler Slow flash fault is £100-300 including labour.

Slow flash High

Boiler Fault Code Slow flash

Also written as SLOWFLASH — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code Slow flash appears across 2 boiler brands and 11 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 running for safety reasons and needs to be manually restarted to try and get your heating and hot water back on. (As reported on Worcester Bosch 24CDi BF)

Pick your boiler brand for the Slow flash fix

Grant Slow flash 5 models Worcester Bosch Slow flash 6 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 27 April 2026