https://www.theverge.com/2018/8/31/17807420/apple-iphone-8-logic-board-repair-program-defective-replacement

Apple quietly announced the launch of a free repair program for the iPhone 8 this afternoon, revealing that a “very small percentage” of units need replacement logic boards due to a manufacturing defect. The logic board is essentially the main printed circuit board of a computing device, containing the CPU, device memory, and other integral components. Apple says its faulty logic boards may have been causing random restarts, screen freezes, and defective startup initiations that prevent the iPhone 8 from turning on properly.

The defect does not affect the iPhone X or the iPhone 8 Plus, and Apple says the affected units include only those sold between September 2017 and March 2018 in Australia, China, Hong Kong, India, Japan, Macau, New Zealand, and the US. You can input your iPhone’s serial number into Apple’s repair page to see if you’re unit is eligible. The program covers iPhone 8 units sold up to three years after the first retail sale of the device in September 2017.