Boiler Fault Code UU/2

Also written as UU2 — same fault.

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

Fault code UU/2 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 that the water returning from your radiators is at an unusual temperature, which usually means the water isn't flowing through the system correctly. (As reported on Ariston Genus 27)