Today I had a call from Waterford, Michigan home owner. She was panicked because her front door would not open. The only way out was through the garage door. Her nephew who was 16 had used force to rotate the door knob previously but this too had stopped working.
I asked her to read what was on her key and she said KW1 this indicated to me that her lock is most likely a Kwikset brand entry knob. (I also had a feeling that it was Kwikset due to experiencing the same issue in the past).
The home owner thought she would need to replace the entire lock and was worried that she would need new keys but, I explained that all we need to do is replace the latch. The latch is the part of the lock that sticks out of the edge of the door and keeps the door closed and locked. Spring loaded.
There are a few reasons the latch fails and one of the biggest is the deadlocking pin breaking. Deadlocking pin is the little additional plunger next to the larger latch plunger. When the door closes, the latch is supposed to go into the strike plate. (metal plate on frame). The deadlocking pin is to remain on the outside of the strike plate pushed in.
If the strike plate is misaligned it may allow the whole latch to enter. This means that the deadlocking pin and the latch are inside of the strike plate. Wrong!!!!
The deadlocking pins job is to keep the latch extended into the strike plate in a fixed manner. Years ago credit cards and the like were used to slip past the latch and depress it in to open a door. If the deadlocking pin is working properly the latch will not retract from pressure. This is why it is important to have your latch correctly positioned for effective security.
If the whole latch is allowed to enter the strike plate it can bind and cause premature failure and lock in the extended position.
There are other reasons that a latch fails and age, use and quality play a role.