Door latch not working

Take the handles off and check whether the square shaft is a good fit in them - if loose then replace the shaft or pack the holes with something rigid. See if the latch retracts enough if you turn the shaft with a spanner or pliers - if not decide whether to replace the latch or increase the rebate for the receiving plate (or whatever its called).

It is surely too near to the edge of the door if it protrudes too much.

If it is one of those cheap and nasty die cast things then it is worth checking that the square hole in it is still intact. I had my main front door fail that way with the initial symptom being hard to open followed by impossible to open because the casting fractured.

If it is sound then you may be able to improve things by shimming the existing square bar or swapping it for a slightly fatter one. Some nicer ones are actually adjustable which is worth checking.

If it was like that from new then they didn't fit it properly.

Simplest solution might be to sink it 0.5mm more into the door - enough that the catch works cleanly but not enough to need to move screw holes.

Or alternatively move the plate it mates with slightly further away.

Do check the internal mechanism first.

Probably be best to tackle it on the doorframe side than have to move the actual lock considering the holes are now drilled. I simply recessed the part of the locking plate a bit more so it could clear the latch when fully retracted. Brian

What kind of latch is it?

e.g. a surface fitted one, a traditional mortice one, or a modern "tubular" one?

I have noticed that as the mechanism wears (especially on budget latches) the amount of bolt retraction can reduce.

Probably also worth taking the handles off and seeing if you can retract it by turning the shaft with pliers. If not, time for a new latch.

The tubular latches sold at Toolstation for about 90p are not very good, get one of the ones that costs about £3.50 they are MUCH better - money well spent!

Last week I decided the our inner kitchen door latch inner handle, leading to the outside, was becoming a bit worn. I had a couple of spares, but of the wrong 'hand'. I decided the simple fix was to swap kitchen door inside handle for the utility inside one, which was identical. No one ever goes in the utility room and closes the door behind them. Might you be able to make a similar swap?