Moving DNS from one Cpanel server to another

We used to run 3 X cPanel servers
1 was a backup server and ran our secondary dns service (ns2)
1 was a webserver (web)
1 was a webserver which also ran our primary dns (ns1)

all worked fine

we have let the backup server go (underutilised) and thought we had switched over our secondary dns to the other webserver

we have the nameserver domain running on ns1 and i edited the dns zone to add a new NS and A entry for the webserver to call it ns3.ourdomain.com

We have bind running on web server

I can query ns3 fine on the server itself but everywhere else isn't seeing it and hence lookups don't work

I am no DNS expert so at a loss as to where to go from here ?

Should the A entry for the ns3 host be pointing to the shared IP or does it need its own IP ?