BMW X7 E70 2007 only over heats if heater not at maximum 84 and max fan

[davidyun]

I know there is so much information I’ve been reading through.

Overheats if heater not full blast 84. Otherwise the fan doesn’t kick to full.
No leaks, burped multiple times and coolant level steady, water pump works.
Could it be something with a relay electronics?
Replaced expansion and hoses to it.
Maybe it’s the temp gauge not opening if heater is not at full?
Heater fan at half or 1 bar still overheats.

I have been trying to install ista for 3 days still a pain in the a. EDIT: Ista working now! Cable connection fixed.

Thoughts?
Thanks!
DA