Have you experienced an Error 53 while restoring or updating to the latest iOS on your iPhone 6.
Help is at hand. Error 53 is caused by a hardware fault. This is probably one of the following:
1. Touch ID Sensor faulty. This was probably caused during a recent screen replacement. The quickest way to solve this is to either, borrow the whole screen assembly from a friends iPhone 6, restore the phone and then never update the iOS, or try and replace the touch ID sensor.
2. Incorrect screw placement during screen replacement. There are four screws that hold the LCD and touchscreen connectors down. If the longest screw is screwed into the wrong hole, it can cause damage to one of the internal layers of the logic board PCB. There isn't much you can do about this one. Apart from beg Apple to replace it under warranty.