Cracked it. Failure to boot was the result of including tboot in the install package set, for some reason or other. It's not needed and removing it does the trick. https://access.redhat.com/articles/2217041 And I thought I was going spare when it worked with one install package set and not another ... When using a kickstart file, the bootloader, clearpart and zerombr directives also need attention. Used without the correct options they will install an MBR which is not exactly desired.