BoilerFaultCodes Block 01 High
Boiler Fault Code Block 01
Also written as BLOCK01 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Block 01 appears across 1 boiler brand and 4 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 an external safety device, such as a heat sensor or chimney flue thermostat, has triggered a shutdown to prevent overheating or unsafe operation. (As reported on Atag Q 25CR)
Pick your boiler brand for the Block 01 fix
Source
Information for the Block 01 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 7 July 2026