So does the pump switch on at all when you lift the lever?
I am right in thinking this is an E61 manual lever group machine? Never seen a Viola before, but it should work the same as all other domestic E61 groups, ie. when you lift the lever you open the 3-way valve in the group, and it also activates the pump via a microswitch.
If theres not even a dribble coming from the group and the pump is running, then therell be a serious blockage internally and youll most likely have to start taking pipes off to find it.
I would first take off the big nut on top of the group and see if theres any evidence of scale. If there is, that will be the culprit but the blockage could be anywhere.