BoilerFaultCodes 9b:70 Low
Boiler Fault Code 9b:70
Also written as 9B70 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 9b:70 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 is notifying you that it has received a request for heat from an external source, such as a thermostat or control system, that is lower than the minimum temperature the boiler is currently programmed to provide. (As reported on Viessmann Vitodens 300-W)
Pick your boiler brand for the 9b:70 fix
Source
Information for the 9b:70 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