Thanks for the question!

The framing gun has a leak, most likely it's one of the Cylinder Seals inside the main body of the gun, or the Head Valve itself is worn (as well as the Head Valve seals).

It's very common for this to happen. Most likely you'll need an o-ring rebuild kit. The nailer is probably pretty dirty as well as debris can wear out the seals and keep the gun from operating. Once you have it apart it's a good idea to clean it out very well in a parts washer, then lube the o-rings up very well, then add a few drops of pneumatic oil and you should be good to go.

You can find the O-Ring Kits for the Bostitch nailers on our site by clicking on the below link:
www.mastertoolrepair.com/bostitch-nailer...ts-c-64_291_292.html

- MTR