Boiler Fault Code 00:4

Also written as 004 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code 00:4 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 This code is not actually a fault, but a status indicator confirming your boiler is configured to control both your radiators and your hot water tank separately. (As reported on Viessmann Vitodens 050-W)