T1 Low

Boiler Fault Code T1

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code T1 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 currently running a self-diagnostic check to ensure the ignition system is sparking correctly before it starts up. (As reported on Worcester Bosch Greenstar Si Combi / i System)

Pick your boiler brand for the T1 fix

Worcester Bosch T1 11 models

Source

Information for the T1 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