LED 4 flash/second Medium

Boiler Fault Code LED 4 flash/second

Also written as LED4FLASHSECOND — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code LED 4 flash/second appears across 1 boiler brand and 1 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 an issue with the sensor that manages your hot water, meaning you will likely only have heating or very inconsistent water temperatures. (As reported on Worcester Bosch 24si II)

Pick your boiler brand for the LED 4 flash/second fix

Worcester Bosch LED 4 flash/second 1 model

Source

Information for the LED 4 flash/second 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