When a door closer will not latch the door

The half-open test comes first

It is the one that catches an under-sized closer, and it costs nothing. From fully open a door has the whole swing to gather speed; from half open it does not, so a closer that is marginal for the leaf will reach the frame without enough left to drive the latch. Set the latch speed before you read anything into the result, though — a latch valve turned too far towards slow produces the same symptom on a closer that is the right size.

1. 1Raise the latch speed first. The latch valve controls the last few degrees, and a door latches on the momentum it still has when it gets there. Set that valve too slow and it works against the momentum rather than with it, which is the commonest reason a correctly sized closer will not shut a door. Turn it half a turn towards faster and test again. Too slow and the door rests on the frame; too fast and it bangs.
2. 2Then open halfway and release. With the latch speed right, this separates a sizing problem from an adjustment one. If it latches from fully open but still stops short from half open, treat the closer as under-sized for that door and go to the sizing question.
3. 3Check what the door is fighting. An external door, a corridor that funnels wind, or a stair core with a pressure difference across it all take force that no catalogue figure accounts for. The same closer that is right on an internal door can be marginal on that one.
4. 4Check the keep and the hinges. A door that has dropped, or a strike plate that no longer lines up, is a door problem rather than a closer problem. The closer cannot pull a latch into a keep it does not meet.

Wide leaves have a hard floor

On a leaf wider than about 1500 mm, a small closer will not latch the door at any setting. That width needs a large unit to pull it closed against the latch. If a small one is already fitted, the answer is a different closer, not a different adjustment.

On a fire door this is not a comfort question. It has to close and latch from any angle it can be opened to, with nothing holding it — that is the definition of a self-closing device, not a preference. A fire door that rests against its frame without latching has not done its job. Fire-door locks are deliberately stiff, so the latch speed usually has to be set faster here than on an ordinary door, letting the momentum carry the latch home. That is also why a controlled closer is specified: it puts its highest force into the last few degrees, where the latch resistance is.