By default, the root password for the vCenter VA will expire after one year of the vCenter VA installation, and this is because the default password expiration password is set to one year, if the password expires, then you are in a big trouble. the following simple steps in the video will teach you how to set the password expiry date to infinite.
Simply login to the VA console using the root account, then issue this command:
chage -M -1 -E -1 root
This applies to vCenter 5.5 and 6.0
I hope that this is helpful