BoilerFaultCodes ALL 99 High
Boiler Fault Code ALL 99
Also written as ALL99 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code ALL 99 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's main computer brain has encountered a critical internal error and needs to be reset or professionally inspected to safely restore operation. (As reported on Sime Brava Slim HE System)
Pick your boiler brand for the ALL 99 fix
Source
Information for the ALL 99 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 7 July 2026