BoilerFaultCodes A0:0 Medium
Boiler Fault Code A0:0
Also written as A00 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code A0:0 appears across 1 boiler brand and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has lost communication with its external thermostat or control unit, meaning it may not know when to turn your heating on or off. (As reported on Viessmann Vitodens 200)
Pick your boiler brand for the A0:0 fix
Source
Information for the A0:0 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