A4 Low

Boiler Fault Code A4

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code A4 appears across 4 boiler brands and 10 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is displaying a memory code indicating that it previously encountered a fault and shut down for safety reasons, though it may currently be working. (As reported on Sime Metropolis DGT 25 BF)

Pick your boiler brand for the A4 fix

Atag A4 6 models Sime A4 1 model Viessmann A4 2 models Vokera A4 1 model

Source

Information for the A4 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 31 August 2026