BoilerFaultCodes UU/tt High
Boiler Fault Code UU/tt
Also written as UUTT — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code UU/tt 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 is struggling to detect the flow of water circulating through the system, which prevents it from igniting to provide you with heat or hot water. (As reported on Ariston Genus 24 MFFI)
Pick your boiler brand for the UU/tt fix
Source
Information for the UU/tt 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 27 April 2026