BoilerFaultCodes 9b:1 to 9b:127 Medium
Boiler Fault Code 9b:1 to 9b:127
Also written as 9B1TO9B127 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 9b:1 to 9b:127 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 an internal configuration error where the target temperature has been set to an invalid value or a internal circuit board fault is occurring. (As reported on Viessmann Vitodens 300-W)
Pick your boiler brand for the 9b:1 to 9b:127 fix
Source
Information for the 9b:1 to 9b:127 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