Key turns but the deadbolt won't unlock — why does it just spin?

A key that will not turn is one problem. A key that turns easily and does nothing is a different one. The cylinder is working, because the key rotates. What has failed is the link between the cylinder and the bolt, so the turn never reaches the bolt.

That link is small and it can break. Knowing which part has gone tells you whether you can still lock the door tonight, and whether you need a locksmith to get in. This guide covers home and business doors only.

First: stop turning the key

Spinning the key over and over will not grab the bolt, and it can wear the remaining parts or snap the key. Take the key out and work out which side of the door you are on and what still works.

If you are outside and the door is locked, use another door if there is one. If there is not, call a locksmith. A locksmith can often open a door like this without drilling, and then repair the lock in the same visit. Do not pry the door or the frame. That turns a lock repair into a door and frame repair.

How a deadbolt connects to the key

On a standard deadbolt, the key cylinder on the outside has a thin flat bar on its back called the tailpiece. It passes through the bolt mechanism inside the door and into the thumb turn on the inside. Turning the key turns the tailpiece, and the tailpiece drives the bolt. Two long screws through the inside half hold the whole lock together.

Many commercial doors and older entry doors use a mortise lock instead: a box set into the edge of the door, with a threaded cylinder screwed into it and held by a set screw. A small cam on the back of the cylinder throws the bolt. The idea is the same. If the cam or tailpiece stops reaching the bolt, the key just spins.

Common causes

• A broken or twisted tailpiece. The most common cause on a residential deadbolt. The key turns, the thumb turn on the inside may still work, but the key no longer moves the bolt.
• Loose through-screws. If the two screws holding the inside and outside halves together back out, the cylinder can pull away from the bolt and the tailpiece slips out of its slot.
• A loose mortise cylinder. On a mortise lock, if the set screw loosens, the cylinder can unscrew a little each time the key is turned until the cam no longer reaches the bolt. A cylinder that turns in the door when you twist it by hand is the tell.
• A broken bolt mechanism. If neither the key nor the thumb turn moves the bolt, the part inside the door edge has likely failed.
• A bolt jammed against the strike. If the key turns part way and then meets resistance, rather than spinning freely, the bolt may be binding against the strike plate because the door has moved. That is an alignment problem, not a broken lock.

A quick way to tell which one you have

• Thumb turn works, key does not: the tailpiece or the outside cylinder has failed or come loose. You can still lock the door from inside, so it is not an emergency, but you cannot lock it behind you when you leave.
• Neither the key nor the thumb turn moves the bolt: the bolt mechanism has failed, or the lock has come apart inside the door.
• The key turns, then stops with resistance: push or pull the door firmly toward the frame while you turn. If the bolt moves that way, the door needs adjusting, and the lock is fine.
• The cylinder itself rotates in the door: a loose mortise cylinder or loose screws. Do not keep using it.

What a homeowner can safely do

• With the door open, check whether the thumb turn throws the bolt. That tells you whether the bolt itself still works.
• Check the two screws on the inside half of the deadbolt. If they are loose, snug them by hand with a screwdriver and test the key with the door open before you close it.
• If the bolt is catching on the strike, look for scrape marks and tighten the hinge screws. The guide on a deadbolt that won't lock covers alignment in more detail.
• Until it is fixed, do not rely on a lock that only sometimes engages. If you cannot lock the door from outside, leave through a door that does lock.

What to leave to a locksmith

Opening a locked door whose key spins, extracting a cylinder, and replacing a broken tailpiece, cam, or bolt mechanism are normal locksmith work. Parts have to match the lock's make and the thickness of the door, and a mortise cylinder has to be set to the right depth or it will loosen again.

If the lock is being replaced anyway, it is a good time to rekey it so it matches your other doors. If the door or frame is cracked or split around the lock, the frame needs repairing as well, or a new lock will not hold.

How it gets fixed, and what moves the price

A locksmith confirms which part has failed, opens the door if it is locked, and then either reconnects and replaces the broken part or fits a new deadbolt. A loose mortise cylinder is often reset and secured rather than replaced.

What moves the price is whether the door is locked with you outside, whether it is a standard deadbolt or a mortise or commercial lock, whether a part can be replaced or the whole lock is changed, whether you want it rekeyed to match other doors, and the time of day. You see a qualitative range up front, and the locksmith confirms the price in person after seeing the door.

If your key turns but the lock will not open or lock, describe the problem on rogerrepair.com and get one locksmith booked. Roger books one vetted local locksmith and confirms the appointment. Home and business only.