Thanks for the reply.
It looks like it is settled down a bit over the weekend, not sure why?
After power up of both servers on the system come up as expected with the mounted file system. A stop of hearbeat on server1 brings in server2 with the file system correctly mounted. The test client keeps the mount ok. restarting heartbeat on server1 switches the file system back to server1, but I now get the error message:
nfssvc: Setting version failed: errno 16 (Device or resource busy)
nfssvc: unable to bind UPD socket: errno 98 (Address already in use)
The client does not keep the mount.
I need to reboot everything to get back a working server.