Tnx a lot man
That put me in the right direction. I also found this post which actually nailed it:
I'm writing in detail in case others might find it useful.
The setup on my machine was:
sda1: W7 NTFS
sda2: FAT32 free space
sda4: encrypted LVM
what I did:
booted up with debian netinst usb, enable rescue mode. After a while it asked me which partition to mount and I choose root and entered the passphrase.
It then opened a terminal as su, and I typed:
mount /dev/sda3 /boot
and that's it. rebooted the machine & it's all dandy