Help fixing grub install

Hi, After re-installing Kubuntu on my (EFI, GPT) laptop (which also has Windows 10), I've ended up with a broken grub. It used to work fine. The problem is that now it boots into grub, with no configuration, just the grub> prompt. I can continue by typing: grub> configfile (hd0,gpt6)/boot/grub/grub.cfg which then brings up the usual menu. But I'd like to know how to configure grub so that it finds it automatically! Needless to say, I have already tried running grub-install /dev/sda after booting. (Which succeeds without error) Any suggestions? PS. I don't want to totally blank the drive, as it shares with a Windows 10 install that I'd like to keep. Thanks Toby