Stiff Door Lock? Possible Causes and Safe Checks

In short:

Start with one test: does the lock work smoothly with the door open? If it does, the door or frame is usually the problem, not the lock.
If it is stiff even with the door open, look to the lock or key: dirt, wear, the wrong lubricant or a worn key.
There is no single "right" lubricant. Lock makers specify different products, and some warn against oil, graphite or silicone. Follow the maker of your lock.
Never force a stiff key. Forcing a jammed lock is a common reason keys snap.

What a stiff lock feels like, and why it matters

"Stiff" covers several different symptoms, and the exact one is a useful clue. Notice which of these you have:

The key is hard to push in or pull out, or catches part-way.
The key goes in easily but needs effort to turn, or turns in a rough, gritty way.
The key turns smoothly until the last part of the turn, when the bolt has to go into the frame.
On a door with a lever handle and multipoint lock, the handle has to be lifted harder than it used to before the key will turn.
The stiffness comes and goes: worse on hot afternoons, after rain, or only on one door.

A stiff lock is more than an irritation. Keys are designed to be turned by hand: EVVA says not to use screwdrivers, pliers or a bunch of keys for extra turning force, and Winkhaus says not to force the key. Pushing harder on a stiff lock is how keys bend and snap. The MLA, the UK locksmiths' trade association, advises getting a lock checked as soon as you feel any difference in how it locks.

The first check: is it the lock or the door?

EVVA's cylinder manual tells installers to check the locking function while holding the door open, so the lock works without any load from the frame. ERA's multipoint guide adds that resistance during operation may mean the fitting isn't right. You can use the same idea as a safe diagnostic:

Open the door and make sure it can't swing shut or be closed by wind.
With the door open, insert the key and lock and unlock it a couple of times, watching the bolt move out and back. On a multipoint door, lift the handle and turn the key as you normally would.
Compare that with how it feels when the door is closed.

What the door-open test tells you
Result	What it usually points to
Smooth with the door open, stiff with it closed	The bolt, latch or hooks are rubbing on the strike plate or keeps. The door may have dropped, the frame may have moved, or the door may be swelling or expanding. See causes by lock type and our guide to a door that locks when open but not when closed.
Stiff whether the door is open or closed	The problem is in the lock or the key: dirt, wear, a dried-out or gummed-up mechanism, a damaged or worn key, or a cylinder that is clamped too tightly.
Stiff only with one particular key	That key is probably worn, bent or a poor copy. Compare it with the original or a spare.
The key won't go in fully	Debris in the keyway, a damaged key, or something already inside the lock. Don't force it.

Possible causes by lock type

A home can have several lock types: lever mortice locks in timber doors, cylinder locks in many aluminium and newer doors, multipoint locks, rim nightlatches and hook locks on sliding doors. Each goes stiff for different reasons. Our guide to mortice, cylinder and multipoint locks explains how to tell them apart.

Cylinder locks (euro-profile, oval and rim cylinders)

Dirt and dust in the keyway. ASSA ABLOY's South African care guide says dirt and grime can damage the mechanism, including the cylinder barrel.
Lack of lubrication, or the wrong product. Makers set intervals: Mul-T-Lock asks for at least twice a year, and more often on exterior doors.
An over-tightened fixing screw. EVVA and CISA both warn that over-tightening the screw that holds the cylinder can make it stiff or jam.
A cylinder squeezed by the door or fittings. Winkhaus says the cylinder must be fitted so that its cam moves freely and the housing isn't jammed or distorted, for example by a door that binds or by displaced fittings.
Wear on the key or the pins, especially on a much-used front or kitchen door.

Lever mortice locks

Dust and debris collecting inside the lock case through the keyhole.
A worn key, or a worn bolt rubbing in its opening on the faceplate.
The deadbolt catching on the edge of the strike plate, a common cause on timber doors that have dropped or swollen. The key turns easily, then tightens at the end.

Multipoint locks

A multipoint lock throws hooks, rollers or bolts at several points along the door edge, so it is very sensitive to alignment. Keeps out of line, a door that has dropped on its hinges or compressed weather seals all make the handle hard to lift and the key hard to turn. The MLA says weather is a common cause of sticking on uPVC doors, because the material expands and contracts with temperature, and also lists dropped doors and worn hinges.

Rim nightlatches

The latch can rub on the staple (the keeper on the frame) if the door has moved. The cylinder's connecting bar also has to be the right length: Yale's rim nightlatch instructions specify how far it should project, and this varies by model.

Sliding-door hook locks

On aluminium sliding doors the hook has to swing into a keeper on the frame. If the door has dropped on its rollers, the track is full of grit, or the keeper has shifted, the hook drags or misses. Everest, a UK door maker, also points out that heat and direct sun can make a door expand enough to affect locking.

Stiff-lock symptoms, possible causes and a safe first check
What you notice	Possible causes	Safe first check
Key hard to push in or pull out	Dirt in the keyway, a worn or burred key, damage to the cylinder face	Look at the key against a spare in good light; look at the keyway entrance for grit
Key turns roughly, open or closed	Dirt, dried or unsuitable lubricant, worn pins or levers, over-tightened fixing screw	Door-open test; check whether a second key feels the same
Tight only at the end of the turn	Bolt rubbing on the strike plate or keep	Look for bright scrape marks on the strike plate and the bolt
Multipoint handle hard to lift	Keeps out of line, dropped door, seals, gearbox wear	Door-open test; check whether the gap around the door looks even
Sliding-door hook drags	Door dropped on rollers, dirty track, keeper moved	Look along the track for debris; see whether the door sits level

Safe checks you can do yourself

None of these involve taking anything apart. Stop if anything feels as though it might bend or break.

Do the door-open test described above. It is the single most useful check.
Compare keys. Hold the key you use every day next to a spare, preferably an original. Look for rounded or flattened cuts, a bend, cracks near the shoulder, or burrs. If the spare works smoothly, the everyday key may be the problem.
Look at the strike plate and keeps. Shiny scrape marks, flattened paint or chewed edges show where a bolt or hook is rubbing.
Look at the gaps around the closed door. An even gap along the lock side suggests the door is sitting square. A gap that is wide at the top and tight at the bottom on the lock side suggests the door has dropped.
Look at the hinges for missing or loose-looking screws, and note what you see.
Wipe visible dirt from the face of the lock with a dry or barely damp cloth. ASSA ABLOY recommends removing dirt, grime and salt deposits from around the end of the cylinder, and says cleaning fluids must not get into the lock or cylinder.
Note when it happens: time of day, weather and whether it's getting worse.

Lubrication: follow your lock maker, not a universal product

You'll find plenty of advice that a particular spray or powder fixes every stiff lock. Manufacturers' own instructions disagree with each other, and the differences matter:

ASSA ABLOY (the group behind Yale and Union) says in its South African care guide that cylinders, lever locks and padlocks should be lubricated with its graphite powder. For exposed moving parts it suggests a Teflon (PTFE) based lubricant, or light mineral oil as an alternative, used sparingly. It warns against silicone-based lubricants because they turn tacky.
Winkhaus tells owners to lubricate its cylinders with special care products and never to use oil or graphite.
Mul-T-Lock specifies its own lubricant for its mechanical cylinders, at set intervals, and says not following its maintenance procedures voids the warranty.
EVVA recommends its own care spray and warns that corrosive cleaning agents or resinous oils can cause malfunctions or failure.
For uPVC multipoint mechanisms, the MLA (the UK locksmiths' trade association) advises a PTFE lubricant that won't attract dirt, rather than standard spray oil.

So identify the lock (the brand is often stamped on the faceplate, cylinder or key) and follow that maker's care instructions. If you can't identify it, don't experiment. And lubricant can't fix a bolt rubbing on a strike plate: if the lock is smooth with the door open, the answer is alignment.

Things that make a stiff lock worse

Forcing the key, or using pliers, a screwdriver through the key's bow or another key for leverage. This is how keys snap. If one does, read what to avoid with a broken key in a lock.
Spraying a general-purpose oil into the keyway. Some makers warn against oil altogether.
Using the key as a door handle to pull a sticking door shut. EVVA lists this as incorrect use, because it puts sideways force on the key.
Tightening the cylinder fixing screw because the cylinder feels loose. Over-tightening is a known cause of stiffness and jamming.
Taking the cylinder or lock apart. Small parts are easily lost, and EVVA recommends that cylinders are installed only by trained staff.
Filing or chiselling the strike plate. It can weaken the frame and hides the real problem.
Leaving the door unlocked because locking it is a struggle.

When to call a locksmith

Call a professional if any of these apply:

the lock is stiff even with the door open;
it is getting worse week by week;
the key has started to bend, or you can see cracks on it;
the door has to be lifted or pushed to lock, which means the bolt is under load every time;
it's your only key, or the only lockable outside door.

The MLA doesn't recommend realigning a door yourself, because on some doors it means dismantling parts of the lock or taking hinges off. A lock repair visit usually starts with the same door-open test, then checks the key, the lock and the alignment of the bolt with the strike. Many stiff locks can be put right by cleaning, correct lubrication, adjusting the strike or keeps, or replacing a worn part; our guide to lock repair or replacement explains when replacement makes more sense. A badly swollen door or moved frame may also need a carpenter or door installer.

As a mobile locksmith in Sandton, we check the lock, door and frame together, at the door.

What to tell or send the technician

A few details make the diagnosis quicker and help the technician bring suitable parts:

A photo of the lock from both sides of the door, and of the door edge showing the faceplate (brand names and numbers are often stamped there).
A photo of the strike plate or keeps on the frame, close enough to show any scrape marks.
A photo of the key next to a spare, if you have one.
The result of the door-open test: smooth or stiff with the door open.
The door material, and whether anyone has recently sprayed anything into the lock.

Questions

Can I just spray some household oil into a stiff lock?

It's better not to. Lock makers specify different products, and some, such as Winkhaus, say never to use oil in their cylinders. EVVA warns that resinous oils can cause malfunctions. Oily residue can also hold dust. Check what the maker of your lock recommends, or ask a locksmith.

Why is my lock only stiff on hot afternoons?

Doors and frames expand and contract with temperature, and a door in direct sun gets much hotter than the air around it. If the bolt or hooks only just clear the strike plate or keeps, a little expansion is enough to make them rub. It points to alignment rather than a faulty lock.

Need a locksmith to look at it?

If this hasn't solved the problem, our lock repairs service covers it. We're a mobile locksmith in Sandton, so we come to your door.

Sources and further reading

ASSA ABLOY South Africa: Product Care and Maintenance — Cleaning, graphite powder for cylinders and lever locks, PTFE or light oil for exposed parts, no silicone; hinge and frame faults load the lock
Winkhaus: profile cylinder fitting and care instructions — Cam must move freely and housing must not be jammed; don't force the key; never use oil or graphite
EVVA: lock cylinder installation and operating manual — Check locking with the door open; over-tightened screw causes stiffness; no tools for extra torque; resinous oils can cause failure
Mul-T-Lock: key and cylinder maintenance — Manufacturer-specified lubricant and intervals; more frequent care for exterior doors and harsh weather
Master Locksmiths Association: uPVC door lock mechanism sticking — Weather, dropped doors and worn hinges as causes; PTFE lubricant; don't realign a door yourself
ERA: Touchkey multipoint lock installation guide — Resistance during operation suggests incorrect fitting; adjustable keeps; door-to-frame gap
Yale (ASSA ABLOY): rim nightlatch installation instructions — Connecting (tail) bar must be cut to a set projection for the lock to work
Everest: patio doors that will not lock — Dropped sliding doors, keep alignment and heat expansion
CISA: cylinder installation guide — Over-tightening the fixing screw can make the lock malfunction or jam
RACV: how to maintain your locks — Signs of strike misalignment; locks that stay stiff after correct lubrication need professional attention