Originally Posted by Clavurion

Was it the additional pre-heater version or just the normal suplementary heater? (Aux heater on the screen option or only Aux ventilation?)

With ignition on remove the fuse or voltage supply connector for at least 20 seconds to reset the possible fault mode. If you want to investigate it properly INPA is the way to go. Besides codes INPA has good live data from Webasto.