Hi, we have the same problem with our new 2018 Qashqui SL Platinum. The steering wheel doesn't heat up and just become slightly warm.
I have it checked by the dealership. They compared it with another Qashqui and found the heating level was almost the same. They told me it might be a systematic design issue. I called Nissan and opened a complain case. Nissan asked me to wait a couple of months then take it again to the dealership, a silly answer to our complaint.
I took the car to the dealership again after 2 months and they told me the same thing as last time.
I'm still in back and forth with Nissan. If this is a typical issue, Nissan is making a false advertisement regarding to this feature.