No coffee comes through the filter.

We have a La Pavoni espresso pump machine (model EP-EPL)
No coffee will pass through the filter.
If the filter holder is in place, without the cofee filter inserted, water will flow through ok. But, if the cofee filter is inserted, no liquid flows through whether there is coffee in the holder or even if it is empty.
We have descaled the machine and ensured that the machine is charged, but this has no cured the problem.