BoilerFaultCodes 4 flashes High
Boiler Fault Code 4 flashes
Also written as 4FLASHES — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 4 flashes appears across 1 boiler brand and 3 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 chip is missing or has lost its connection, meaning the system cannot identify which model it is and has stopped working for safety. (As reported on Worcester Bosch Greenstar 42CDi)
Pick your boiler brand for the 4 flashes fix
Source
Information for the 4 flashes 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