3rd party SSD won't boot

Hi,

I have a Mid 2012 13 inch macbook pro that's been running successfully with a hybrid drive (3rd party) for the last few years. Recently, the operating system crashed and the hard drive is no longer recognised in recovery mode, so I purchased a 500GB samsung SSD to go into the machine.

I can successfully install Mountain Lion or El Capitan on the new SSD, but it never boots. I simply get any of folder with question mark / cancel symbol or flashing between the two when trying to run off that drive. Here's what I've tried

1. Boot in recovery mode, format drive as 1 partition (Mac OS journaled), and then install OS X. This works successfully until trying to boot from the SSD.
2. Boot in recovery mode and try and restore from time machine backup. This fails as it cannot create a recovery partition on the drive.
3. I've installed Mountain Lion successfully on an external USB drive, and have it up and running, from there, I downloaded the El Capitan installer and installed onto the SSD, which worked fine, but as soon as it came time to boot from the SSD, no dice.
4. I've created a USB installer from the El Capitan installer (using createinstallmedia), then used that USB drive to install to the SSD, and it all works to the point of trying to boot from the SSD, and then, no dice.
5. Throughout this process, Disk Utility can successfully see and partition the SSD, and Verify Disk has never returned any errors, so as far as I can see, it doesn't seem to be hardware issue, but I cannot get OS X to boot from the disk (it boots fine from the USB I installed to).

Any ideas?