I have a millennium model of the La Pavoni professional. I've had the machine 4 years and have enjoyed every bit of it. A year & a half ago, I changed all the gaskets. Recently, the grouphead gasket came out & cracked when I re-inserted it. Oh well. The other day my replacement gaskets (bought the whole set) came in & I went to work on the grouphead gasket. 9 mornings without my 2 daily doubles is enough.
I inserted the new group gasket into the grouphead with the help of a bicycle tire lever. All is well so far.
I wanted the piston to be in the correct position with respect to allowing water in, the insert screen, ect. So I followed the instructions that came with the gaskets (from European Gift & Housewares) that said I should "tighten the lower retaining nut (raising the lever some) all the way down. Then back off two full turns (one turn for pre-millennium models)" Then install upper retaining nut & tighten against the lower nut.
I did this 4-5 times and every time I pulled a shot the insert screen & grouphead gasket would drop out of position--rendering the machine useless for another shot. Eventually, I came to the conclusion that the only thing that could be pushing my insert screen & gasket out of place every time was the piston itself.
The "backing off" of the lower nut has the effect of making the piston shaft longer which means the piston goes down farther before the lever bottoms out.
So I lowered both upper and lower retaining nut all the way & tried again. At the moment it seems to work--at least the grouphead gasket and insert screen stayed put. I hadn't really noticed where the retaining nuts were positioned before.
So, finally my question: Can/should I leave the upper & lower retaining nuts at the non-recommended spot?

One detail: when the gasket broke two weeks ago, I removed the piston & checked to see if it had loosened like I read here can happen. It was fine.

Mine is tightened all the way down. When I replaced my gaskets, I took notice of this and put it back that way. I have a pre millennium machine but that shouldn't matter.


*edit*
Here is what it says at www.pavoniexpress.com:

"Screw the chrome retaining nut all the way down on the piston shaft, then screw on the chrome cap nut."

Thanks for the link back to that site. I used that site as a reference back a year and half ago & that's probably why I didn't have the issue before. Now I'm reminded to go and de-scale. It's been 6+ months.

Is there any chance you installed the lever upside down? The piston is the only thing that could be pushing the screen out.

I've always done a half turn on my machine. I'm not even sure now where I got that idea from, but it works just fine, has for years.

BTW, when installing that gasket what I like to do is remove the basket from the PF, then put the gasket and screen in the PF and lock the PF in as I would when making a shot. Quick and easy.

Own/ed both the millenium and pre millenium versions and yes, both nuts were in the "all the way down" position, so to speak.

The bottom line is that if your gasket and screen are now not popping out, you are getting a good flush of water when the lever is fully raised, and you feel good resistence and pressure on the downward pull without leakage, then you are in business.

Along with a bit of temperature management 'by feel', these are the only things the pav needs to pull a pretty speccie shot.