BoilerFaultCodes 2 04 Low
Boiler Fault Code 2 04
Also written as 204 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 2 04 appears across 1 boiler brand and 9 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is having trouble communicating with the solar energy system because a heat sensor is disconnected or faulty, which may stop the solar panel integration from working correctly. (As reported on Ariston Clas One)
Pick your boiler brand for the 2 04 fix
Source
Information for the 2 04 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