I had the same problem. After changing the metal sheet with the home button connection cable on it several times to no avail I swapped the home-button for a button laying around in the shop, possibly the original one and it worked.
Anyone know if the same goes for iphone 5s where you swap home button? Got a customer with working touch ID but defective button but don't want to have to put the original back in every time she updates.
If there is no workaround for this problem in the future this is a serious threat for people with a shop. Simply rip a home-button and you will end up paying for someones iphone 6 :-/