How much does it cost to fix boiler error code 400?

Typical repair cost for the boiler 400 fault is £450-£700 including labour.

400 High

Boiler Fault Code 400

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code 400 appears across 2 boiler brands and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's main control unit has developed an internal electrical fault, meaning the computer that manages the heating system is no longer working correctly. (As reported on Viessmann Vitodens 100-W B1GA)

Pick your boiler brand for the 400 fix

Ideal 400 1 model Viessmann 400 1 model

Source

Information for the 400 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 7 July 2026