Can my recovery partition be used after upgrade?
Solution 1:
"Note: If the manufacturer set up your PC to run from a compressed Windows image file (also known as Windows image file boot or WIMBoot) and included the option to restore factory settings, that option will no longer be available after you upgrade to Windows 10."
Found under "Can i go back to my old operating system"
Microsoft Source
But if you made your HP recovery discs prior to upgrading to W10 you can use those to reinstall the previous operating system.