Ext’ Interlock Off Unknown

Boiler Fault Code Ext’ Interlock Off

Also written as EXTINTERLOCKOFF — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code Ext’ Interlock Off appears across 2 boiler brands and 2 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Pick your boiler brand for the Ext’ Interlock Off fix

Ideal Ext’ Interlock Off 1 model Keston Ext’ Interlock Off 1 model

Source

Information for the Ext’ Interlock Off 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 31 August 2026