d8 Medium

Boiler Fault Code d8

Also written as D8 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code d8 appears across 3 boiler brands and 12 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 external signal or safety switch connected to it that is currently reporting an error, meaning the system has paused to prevent operation until the external issue is resolved. (As reported on Viessmann Vitodens 242-F B2UA)

Pick your boiler brand for the d8 fix

Alpha d8 9 models Remeha d8 1 model Viessmann d8 2 models

Source

Information for the d8 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