BoilerFaultCodes E434 High
Boiler Fault Code E434
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code E434 appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is struggling to accurately measure or regulate the flow of water inside the system, which is causing it to stop heating as a safety precaution. (As reported on Navien NCB)
Pick your boiler brand for the E434 fix
Source
Information for the E434 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