My Vev Vigano Kontessa 12 cup espresso maker does...

Question

I recently purchased a 12 cup Vev Vigano Kontessa espresso maker. The directions that came with the product looked pretty simple and I have folowed them exactly. I am having a problem because not all of the water is being forced through into the pot. I'm getting approximately half of the coffee that it is supposed to make. I can't figure out why there is not enough pressure to force the water through. I purchased the correct coffee (illy espresso fine grind, cafe macinato). I tried low, med and high heat on my gas stove. I tried running just running water through (with no coffee) and it seemed to work fine. All the water came through and filled up the pot. Is there some trick to using this that I'm not aware of?