How much does it cost to fix boiler error code T4?

Typical repair cost for the boiler T4 fault is £180-350 including labour.

T4 High

Boiler Fault Code T4

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 27 April 2026

Fault code T4 appears across 1 boiler brand and 11 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 switch between providing heating and hot water because of an internal valve check failure. (As reported on Worcester Bosch Greenstar Si Combi / i System)

Pick your boiler brand for the T4 fix

Worcester Bosch T4 11 models

Source

Information for the T4 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