BoilerFaultCodes T.03 High
Boiler Fault Code T.03
Also written as T03 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code T.03 appears across 1 boiler brand and 12 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's fan is struggling to start or run at the correct speed, which is preventing the boiler from firing up for safety. (As reported on Vaillant ecoTEC plus)
Pick your boiler brand for the T.03 fix
Source
Information for the T.03 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