how can i stop the freezer leaking water occasionally?

what is causing the freezer part of my fridge-freezer to leak water occasionally from under the door? it has been repaired by the engineer once a couple of months ago and now it has happened again! luckily I have an extended guarantee plan but he wasn't really sure of the cause last time. All is ok with freezer temperatures etc but it seems to be something to do with the ice maker. There is no water coming from inside. Fridge freezer is an LG model GWL227HSYA (not plumbed into water supply) It never happened at all until a few months ago and it is over 5 years old.