As said above, not difficult to replace, just awkward due to the lack of space. I changed mine out last year due to a similar fault code. The union that the pressure switch screws onto is like a tyre valve, when you unscrew the sensor it self-seals and when you install the new one it depresses and opens the valve again. You shouldn't need a re-gas unless the system has been leaking through the faulty pressure sensor.
Hope this helps!