Overheating issue in new iPhone 16

Since you state that this is a brand new iPhone, these conditions are normal. Certain related tasks including indexing may continue in the background, in which you may experience an increased thermal temperature. When the setup is fully complete, your iPhone will return to normal conditions.

But also it’s normal for your iPhone to exert some heat when charging. If you do not receive a message with a thermometer, you can continue to use your iPhone normally.

"Iphone16 hot when charging: Brand new trying to set it up. Gets hot when charging"

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Update this First:

iOS 18.3 has just been released, as of this reply. So, back up your iPhone to a computer(Mac or PC), and then perform the update. Having baked it up, you'll have something to restore it from, should something go wrong after the update.

Cool Down the iPhone:

For a few hours, perform the following...

• Power Off: the iPhone for a bit
• Unplug: any Cables
• Place it Atop: a Laptop Cooler
• Keep it in: an open space
• Keep it Out of: direct sunlight