Hi Bob....first off, the Liberty has the pstat located directly under the boiler, upside down, inside the base collar. Before major excavations....there is a stand pipe above the pstat which goes into the boiler and the top of the pipe is designed to be above the water level to give a pressure reading of the steam. When you descale the descaler may not get into the pipe. You can remove the boiler from rest of the machine by removing the nut on the top center and pulling the boiler off the machine then clean this stand pipe by hand (or use a syringe to put descaler into the pipe and then flush). If the boiler does not seem to want to come off hit the nut on top with a wood mallet and this should jar it loose. this gets you in to the top and after reassembling with new boiler gasket (and cleaning the groove etc) you can test the machine to see if this helped the pressure.
The pstat is a fairly fancy affair with a ring adjustment and sometimes temperature or pressure values printed on a paper band around the body of the pstat. To remove the top of the machine from the collar you back out the small screw on the back center top of the collar and remove the big nut on the base in the center...you don't have to take out the 3 smaller bolts....this gets you into the electrical controls inside the collar to change the pstat setting....unfortunately it all has to be reassembled to test and then taken apart and reassembled ad infinitum. I recall an orange vintage MicroCim that I was in and out of that collar at least 25 times

so you will only have 24 to go and we'll be even!