Boiler Fault Code 1 03

Also written as 103 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 1 03 appears across 1 boiler brand and 14 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 move water through the system, usually because there is trapped air, a closed valve, or a blockage preventing proper flow. (As reported on Ariston Clas HE Evo)