Has your iPhone 6 been bricked? Has it ended up as useful as a brick after you had a repair done and then updated your phone to the latest iOs? This is intentional by Apple for you having chosen to have an independant repair shop work on your iPhone. You phone is now a brick and there is nothing anyone can do about including Apple.
How do you get error 53? Error 53 happens when you drop and break the screen on your phone or you somehow break the home button intself. Then you choose the much cheaper and quicker route of repairing your iPhone at a local repair shop other than Apple.
The phone tech is supposed to be super careful and remove your current home button and its flex cable from the old broken glass and transfer it over to the new screen. That home button is paired with that perticular iPhone so that the fingerprint security feature will work. If that home button or its flex cable is torn or damaged it would need to be replaced.
In the iPhone 5s which has fingerprint security you could simply chanage the home button and its flex cable and the phone would continue working as usual except the fingerprint security feature would just not work anymore. The home button would still function like a home button should.
If you do that in an iPhone 6 or 6 Plus you will have a problem the next time you update the iOs. If you had to replace the home button and its flex cable then when you are updating it you will get Error 53 because the home button doesnt match the device. Congratulations your phone is now a brick.
There are Attorneys currently gathering people for a class action suite against Apple. This problem has just begun and I think it has a long way to go before Apple is forced to do something better than it is doing now.