Boiler Fault Code 5B:0

Also written as 5B0 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 5B: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 detected that the hot water cylinder is connected directly to the unit, but there is likely a communication error or a faulty sensor preventing it from heating your water correctly. (As reported on Viessmann Vitodens 200)