How much does it cost to fix boiler error code Ext’ Interlock Off?

Typical repair cost for the boiler Ext’ Interlock Off fault is £90-180 including labour.

Ext’ Interlock Off High

Boiler Fault Code Ext’ Interlock Off

Also written as EXTINTERLOCKOFF — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

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.

Most common meaning Your boiler has stopped working because an external safety device or room control connected to it has been triggered or disconnected. (As reported on Ideal Evomax)

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