As you know ftp servers normally wont allow to login as root user or any of the local user (Example : daemon,bin, sys, nobody…etc) due to security and preventing the ftp servers from ftp brute force scanner attacks. If you still want to enable root user login on vsFTP for some reasons, here is a short tutorial which allows you to do that.
Enabling Root User Login On VSFTP
SSH your server as root and then search for the files ftpusers, vsftpd.users (or) user_list (on Centos the locations should be under the /etc/vsftpd or under /etc). Edit the files on your favorit editor and remove the ” root ” from the list of users. Now edit the /etc/vsftpd.conf file and enable/uncomment the following two lines :
# vi /etc/vsftpd.conf
userlist_file=/etc/vsftpd/vsftpd.users (if exist)
Restart the vsftpd server to load with the new configuration.
# /etc/init.d/vsftpd restart
Now try login as root via ftp and see how it goes.