My FBH/AHCM Auxiliary Heater is not working

First, check for faults. Fuel Prime or Check Operation functions may be required after a long period of inactivity.

Only partial diagnosis of the AHCM / FBH was implemented by Land Rover thus available via the OBD port. The Webasto Thermo Test Software grants access to further functionalities and is connected directly to the unit. More details here;

https://disco3.co.uk/wiki/Fuel_Burning_Heater