I think I've had this issue before but have forgotten to fix it.
This is a DVR so doesn't get rebooted that often. I'm assuming that the issue occurred after a recent kernel upgrade.

I can't boot and I end up getting dropped into Busybox. I believe that my boot partition is full from too many old kernels but I can't remember how to delete them from the Busybox interface or from Grub.

Can anyone help please?