P.03 Low

Boiler Fault Code P.03

Also written as P03 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code P.03 appears across 3 boiler brands and 20 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 operating in a diagnostic test mode rather than a standard fault, meaning it is running at its maximum heating capacity to help a technician check its performance. (As reported on Glow-worm Betacom4)

Pick your boiler brand for the P.03 fix

Glow-worm P.03 12 models Heatline P.03 6 models Vaillant P.03 2 models

Source

Information for the P.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 7 July 2026