From past couple of weeks my phone heat up alot whenever it hypercharge on 30w even if phone is idling. I tried with bluetooth off ,wifi off , airplane mode on. Still phone is heating up while charging.
Do you get the same issue on other USB port in case you haven't tried already?
My phone does get warm when charging with Hyper-Charge, but it's only for a short-time. When it's fully charged, it's back to the normal temperature.
The other thing to try is someone suggested to turn off the system lighting in the Armoury Crate.
The heat is normal during fast charge. If its way beyond as per your personal experience you can visit the service center to have a check.
Do not heat is really common while fast charge, but at a certain extent. Also, it should be only during charging.