BoilerFaultCodes 6.4.3 Water level control High
Boiler Fault Code 6.4.3 Water level control
Also written as 643WATERLEVELCONTROL — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 6.4.3 Water level control appears across 1 boiler brand and 2 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 pressure inside the system is critically low, so it has safely shut itself down to prevent damage. (As reported on Remeha Quinta 30)
Pick your boiler brand for the 6.4.3 Water level control fix
Source
Information for the 6.4.3 Water level control 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