Evening gents from the land down under

First off love the forum , ive used it now a few times to gain some much needed infomation and has help alot.

However im stuck on some VRV II gear , Now im not asking for you guys to fix it but i really need to do some brain storming and gain some more angles to attack it from.

Story go ,

I have a multi story building and ive had a 3 Pipe branch box fail mechanically ( Blocked / Stuck solenoid valve ) on a floor , so ive been able to replace it. Now ive kept the same PCB installed however when power the floor back up i didnt have the B/Box connected to power so its come back with communication fault.

After realizing i re power it back up but this time it took the whole level out on a U4 fault , After some playing round i was able to get the floor back minus the unit ive been working on but the outdoor ( 1 master 1 slave ) its still stuck with a U4 fault and will not run

To date ive carried out a
- Reset of the condensers
- Removed the unit ( B/Box + evap ) out of the dasiy chain loop physically
- Tried codeing out the Master unit , incase it had a issue

But with no luck , this was a late afternoon issue so i didnt really have to time to get right in there.

My question is can you guy suggest some ideas and things to check , Voltages for the main PCB. i beleive its 18vdc ?

I dont know about your Daikin Tech but ours is a 1hr wait each time and im not the type of guy to be standing round playing with my self waiting for a call

Any help would be great , Cheers