Apple announced that it had discovered that a "small percentage" of iPhone 8 models contain logic boards with a manufacturing defect. If your unit has this defect, Apple says that it will repair your device for free. To determine if your model is eligible, click on the sourcelink found at the bottom of this article and punch in your handset's serial number where indicated. To find the serial number on your iPhone 8, go to Settings > General > About.
 
According to Apple, defective units are apt to experience random reboots, freeze up, or not boot up. If your phone is one of the defective models, you can have it repaired by an authorized Apple Service Provider, brought to the Apple Store's Genius Bar, or you can call Apple Support (for that option, click on this link) and arrange to have your iPhone 8 mailed to Apple.
 
Affected units were sold in the U.S., Australia, China, Hong Kong, India, Japan, Macau and New Zealand between September 2017 and March 2018. Note that Apple iPhone 8 Plus models are not part of this repair program.
 
If you are going to take your device to an authorized repair center or the Genius Bar at the Apple Store, you need to back up your phone to iTunes or iCloud. Bring your sales receipt (if available) along with your Apple ID password and personal identification.
 
If you're mailing your iPhone 8 to Apple, unpair your device with any accessories, back up iOS and turn off iMessages by going to Settings > Messages. Apple suggests erasing your handset by going to Settings > General > Reset > Erase All Content and Settings. Disable Activation Lock and remove your SIM card.
 
It is extremely important to note that if your iPhone 8 has another issue, like a cracked screen, that issue will need to be taken care of before the logic board is replaced. And that could leave you with an unexpectedly high bill for a "free repair." Apple has already been called out about this in the past, charging huge amounts for minor screen issues that had nothing to do with a $29 battery replacement. It is probably best to check with Apple before authorizing any repair.