An F BER rating is pretty poor but you would sink up to €80k to bring it up to spec. (Windows, doors, insulation, heating system, new boiler etc) but you could get some grants etc and otherwise a great house in a good location with 4 bedrooms a garage and decent garden.F seems very, very low for a house in that condition.
I will admit, my knowledge of BER is sketchy at best, but I suspect the fact that it's got single glazing, possibly not much insulation in the attic, a poorly insulated flat roof and a crap old boiler be the biggest contributors?
They have done all the nice cosmetic stuff internally but you can do external insulation which would really help.