How much does it cost to fix boiler error code 594?

Typical repair cost for the boiler 594 fault is £120-250 including labour.

594 High

Boiler Fault Code 594

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code 594 appears across 2 boiler brands and 4 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 get enough fresh air for the combustion process, usually because the air intake vent is blocked or insufficient. (As reported on Grant Vortex Eco)

Pick your boiler brand for the 594 fix

Grant 594 1 model Navien 594 3 models

Source

Information for the 594 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 31 August 2026