I have a door handle where the upper screws are constantly working themselves loose. Should I get longer screws, use polyfilla in the screw holes, or something else? The doors are quite thin, made of board I think (not solid wood).
The door is probably made of some type of composite pressed wood material. The screw holes have become mostly stripped out so they no longer can hold tight.
The best fix is to remove the handle temporarily and then clean out loose debris out of the holes. Carve a slightly tapered peg from a piece of pine board that is the shape of the hole and will just start into the hole by light touch. Coat the peg with yellow carpenters wood glue and then pound the peg down hard into the hole. Let the glue dry for a day and then cut the protruding part of the peg off flush with the door surface. To reinstall the handle drill new pilot holes for the screws of the proper size. Then screw into these fresh holes. Should be like new.