A push bar is code-required hardware on a door that serves as an emergency exit. People also call it an exit device or panic bar. You open the door with one motion. Push against the bar, and the latch releases. You never turn a knob or hunt for a handle.
Building and fire code require push bars on most high-occupancy exit doors. This covers public assembly spaces, schools, and other crowded buildings. The bar lets people leave fast in an emergency. No one should ever chain or block an exit device. It has to open every time, without fail.
Why does a push bar stop latching?
Broken hardware causes the problem sometimes. More often, the top and bottom latches drift out of adjustment. Daily use vibrates the door, and the latches creep out of line. A technician can reset them to the right position.
Forcing the door makes things worse. Each hard shove loosens the hardware. Loose hardware pushes the latches further out of alignment. That misalignment leads to sticking and locking problems.