Thanks for the quick response Gizzie

The PXE service is working fine within the NSX-V environment so I know that all settings in DHCP etc are all correct.  When the machine is migrated across to an NSX-T host and connected to the corresponding segment (which is bridged to the NSX-V logical switch) then PXE stops working.  No network changes have been made to the machine, and I can ping and RDP to the machine so I know that the bridging is working fine.