Hi,
This problem could occur due to to two problems.
1)Blockages in the valves.There are many valves present that will cause this issue.
When it is blocked due to dust particles it will block the flow.Check in the the diagram of how
to separate the La Pavoni.Apply some air pressure at the valve knob endings and the flow turnings.
2)Piston may to block the flow.So take it clean and place it properly.
Here is the parts diagram which will help you take apart the La Pavoni.
For clear picture and more details:
http://www.lapavoni.it/PDF/RIC_EuropiccolaProfessional.pdf
http://www.google.co.in/images?um=1&hl=en&tbs=isch:1&&sa=X&ei=_PCRTIzsCsT68AaylNXABQ&ved=0CCMQBSgA&q=La+Pavoni+Europiccola+parts+diagram-1&spell=1&biw=1152&bih=672
post a comment for further assistance.
Thank you for using fixya have a nice day:-)