How much does it cost to fix boiler error code 740?

Typical repair cost for the boiler 740 fault is £120-200 including labour.

740 Medium

Boiler Fault Code 740

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code 740 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 external temperature sensor is reporting an issue, which may cause it to run inefficiently or struggle to heat your home correctly. (As reported on Navien NCB 28 HE)

Pick your boiler brand for the 740 fix

Navien 740 7 models

Source

Information for the 740 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