BoilerFaultCodesTechnical description
Accesory Module is blocking burner operation
What causes this fault?
This code occurs when an external control device, such as a smart thermostat or a zone valve, is sending a signal to the boiler that prevents it from firing. The boiler is technically ready to work, but it is being 'blocked' by a command from an accessory that may be malfunctioning or incorrectly wired. In many cases, this is caused by a communication failure between the wireless receiver and the boiler itself.
DIY fix possible
Check your external room thermostat or smart home app to ensure it is calling for heatReplace the batteries in your wireless thermostat or programmerEnsure any underfloor heating zones or external pumps are switched on and functional
Find a Gas Safe engineer
Search the official register →