Boiler Fault Code 1 03

Also written as 103 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code 1 03 appears across 2 boiler brands and 17 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that water is heating up too quickly because it isn't circulating through the system properly, causing it to shut down for safety. (As reported on Ariston Genus HE)