BoilerFaultCodes Flashing 40 Low
Boiler Fault Code Flashing 40
Also written as FLASHING40 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code Flashing 40 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 Your boiler is struggling to work out the outside temperature because there is a problem with the external sensor or its wiring. (As reported on Heatline Capriz 25/28)
Pick your boiler brand for the Flashing 40 fix
Source
Information for the Flashing 40 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