I wondered if anybody could please help !!

I have recently taken over a maintenance of a Vrf 2 x pipe system consisting of LG
8 x ARNU15GCEA4 Floor standing units linked to
1 x ARUN120LTE4 Condenser
1 x wall controller

All units work well in cooling mode.
As soon as you change to heating the Heating icon displays for about 20 secs then the controller goes blank, there is no summer/winter switch fitted in the condenser.
The same happens if you change the mode from the centralised controller.
Auto mode say 30c set point, controller stays on auto but no heat from units

LG suggested i put the controller on the 1st unit and see what happens from there but i ran out of time, there is a trend system linking a couple of the other systems but this one appears to not be linked although trend are coming in to check.

Has anyone got any ideas of anything else i can do to check on the system ?