Boiler Fault Code 317 A3

Also written as 317A3 — same fault.

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

Fault code 317 A3 appears across 1 boiler brand and 3 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 an electrical fault with the internal sensor that monitors the safety of the exhaust gasses, causing it to automatically shut down to prevent unsafe operation. (As reported on Worcester Bosch Greenstar CDi Compact)