Seized & Jammed Lock Opening: preparing for the visit

The key turns a full circle without any resistance and the deadbolt stays exactly where it is. There is no click, nothing moves behind the face of the lock, and the door is as closed as it was before you touched it.

Worth answering before the call

What kind of lock is it: deadbolt, knob, lever, mortise or keypad? Which side of the building does the door face, and is it near a salted driveway? Do you have identification, a lease or a management contact for the property?

The lever on our shop door goes down but the latch does not pull back. Is that a lock problem?

It usually points to the mortise case rather than the cylinder, and it is a common complaint on commercial doors. Inside the case a return spring, a worn hub, or another part of the latch's drive path can have failed, so the lever moves without driving the latch. The locksmith gets the door open, draws the case out of the door edge, replaces the worn part, cleans and greases the contact points and refits everything, then tests lever, key and thumb-turn together.

My key turns all the way round but the bolt stays put. What has broken?

The key and cylinder are doing their job; the bar behind the cylinder that drives the bolt, called the tailpiece or cam, has broken, slipped or twisted out of engagement. It is a small part. The locksmith retracts the bolt through the mechanism or removes the cylinder to reach it, then fits a tailpiece of the right length and profile. Your cylinder and keys are unchanged afterwards.