BoilerFaultCodes E01-603 High
Boiler Fault Code E01-603
Also written as E01603 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code E01-603 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's built-in pressure tank is no longer able to manage the expansion of water as it heats up, which is causing your system pressure to fluctuate and force the boiler to shut down. (As reported on Worcester Bosch 24i RSF)
Pick your boiler brand for the E01-603 fix
Source
Information for the E01-603 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 7 July 2026