Pressure gauge on my pump stuck at one value, what is wrong?
Considering it's supposed to be sealed you can get quite a lot of muck in a pressure gauge -- maybe dirt collected on the valve.  That's probably what's causing your gauge to stick. The cause of the initial head jamming may have been similar.

I lost a tyre to a blowout when the gauge on my Road Morph was very reluctant to go up.  I took the gauge to bits (one rather subtle screw/cap which also allows me to set the zero point) and cleaned the spring, the piston and the scale that shows through the window. I didn't oil/grease anything, as the piston felt like it hadn't been greased to start with. It seems to move freely now.