BoilerFaultCodesTechnical description
External heating program changeover applies to heating circuit without mixer
What causes this fault?
This fault occurs when an external control device, such as a smart thermostat or timer, sends a signal to change the heating program for a specific part of your system that isn't set up to understand that command. The most common reason is a configuration error in the boiler's software where it thinks it should be controlling a specialized mixing valve that doesn't actually exist. It can also be triggered by a loose wire or a faulty connection between your external room thermostat and the boiler's internal control board.
DIY fix possible
Check any external heating controllers or smart thermostats for conflicting schedule settings.Perform a simple reset of the boiler using the power button to clear the communication glitch.Verify if any external 'party mode' or 'holiday mode' switches have been accidentally toggled.