If you are having trouble opening a lock with your key, especially an exterior lock, then your first instinct shouldn’t be to call a locksmith, it should be to grab a can of lubricant spray.
Over the years, I have been called out to numerous customers who have asserted that they had keys that no longer worked only to discover that all that was required was a little lubrication. Locks can accumulate grit and lock up when exposed to the elements; lubricating the lock cylinder will often free up the mechanisms in the lock and have it working in seconds.
The important thing to remember about locks is that they are made up of a serious of small moving parts. When you insert your key into the cylinder, your key will push up a series of pins which, in turn, allow you to turn the key and unlock the lock. Over the course of time, locks can accumulate dirt and even corrosion just like anything else, especially an exterior lock. This can cause the lock’s parts to seize and the key will not open the lock.
The first thing that you should do in the event that you encounter a problem with a key is spray the lock’s keyway with a lubricant such as WD-40. If the issue with the lock is an accumulation of grit in the mechanism then the application of a lubricant should free up any seized parts.
In addition to spraying the keyway, I also suggest that you spray the latch and the bolt with a lubricant. Spraying these parts will insure that your door opens, closes and locks more smoothly.
As with anything else, there comes a time when a lock has just accumulated so much grit and corrosion that no amount of lubricant will get it to work again. If lubrication doesn’t work then the best thing to do is to call a locksmith.