It’s impossible to cover all the different sorts of door locks, latches and fittings in one article here so we’ll concentrate on the more modern internal door latches that you’re likely to find in the home. Many of the principles can be applied to older locks too.
The handle is attached, usually by a small screw known as a setscrew, to a metal spindle which goes through a square hole in the lock mechanism. When the spindle rotates, it moves the latch bolt in and out of the strike plate (the metal plate) which is fitted into a rebate (slot cut in the wood) on the frame.
Test to Find the Problem
The first part of fixing any door latch is to find out why it’s not working in the first place. Open the door then turn the handle back and forth, watching the action of the mechanism to see if it goes in and out properly. Also turn it to retract the catch and then let it go, to see if it returns to the closed position.
If it all appears to be working smoothly with the door open but the latch is not holding the door closed properly, then the problem may be with the door or the strike plate. Lift the door up to see if there is a lot of movement in the hinges, in which case the door may have to be re-hung.
Striker Plate Fix
If it’s not that, take a close look at the latch as you close the door and try and see or feel where it’s getting stuck or not mating properly with the strike plate. Look for scratches or shiny parts of the strike plate which will show where the bolt is catching the plate instead of going into the hole.
You can fix this by filing the edges of the hole down to give the bolt more room if necessary. If the amount you need to take off is more than a millimetre or two, then you will be better off removing the plate and repositioning it. This will probably mean chiselling out a little more wood either above or below the existing aperture. You will also need to fill in the old screw holes with wood filler so that the screws will go into their new location. New screws are a good bet too.
Sometimes, because of door shrinkage, the bolt isn’t meeting the strike plate, it’s too far away, although this is less of a problem with modern internal doors as they are rarely made from solid wood. Fix this by removing the strike plate and putting a piece of wood of the correct thickness behind it. When replacing the strike plate you will have to use slightly longer screws.
Going back to the beginning when the first test was done, if the door latch itself was very stiff, the problem could be that the handles are too tight on the spindle. Slacken the setscrew in the handle to move one of the door handles back a little and retighten, If that doesn’t fix it, then the problem will be inside the lock and it will have to be repaired or replaced.
If the handle is turning but the bolt isn’t moving then again there is something up with the lock mechanism. To remove it, take one door handle off and pull the other one through from the other side with the spindle. Then remove the screws above and below the bolt on the edge of the door and the lock should slide out of the door.
Latch Replacement or Repair
You could then take it to a locksmith for repair but they only cost a few pounds so it may be easier to replace it. There are different sizes, types and lengths of lock so take the old one with you to make sure you get the right one. Replacement is the reverse of the removal procedure.