How much does it cost to fix boiler error code E777?

Typical repair cost for the boiler E777 fault is £150-300 including labour.

E777 High

Boiler Fault Code E777

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code E777 appears across 1 boiler brand 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 has detected that a safety device installed outside the main unit is reporting a dangerously low water level, preventing the boiler from starting to protect it from damage. (As reported on Navien NCB 28 HE)

Pick your boiler brand for the E777 fix

Navien E777 4 models

Source

Information for the E777 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