BoilerFaultCodes E594 High
Boiler Fault Code E594
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code E594 appears across 1 boiler brand and 7 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's computer memory has encountered a serious internal error and can no longer process instructions correctly, meaning the unit cannot operate. (As reported on Navien LCB700)
Pick your boiler brand for the E594 fix
Source
Information for the E594 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