I have the same machine and have always had to do the handle "up-down dance" to get rid of the air/steam before a proper pull. I just think that is the way the Pavoni is.

Same here, and it's the same on my La Cara and Pavoni as well, sometimes preinfusing for longer, like 30 seconds, helps.

Mike said,

Some of the early "Millenium models" has nylon pistons which tended to unscrew and reduced the group capacity. The solution is either to screw it back in or replace with one of the later brass pistons.

This mirrors my experience. Eventually the plastic piston works loose and I have to remove it and tighten it. Some plumbers tape applied to the thread seems to hold it better. I was having the same pre-infusion problem as the OP today until I did that little bit of maintenance. Now it works fine again .

Usually the lever in the up position allows plenty of water to enter the group. I generally have no need for the Fellini move.

I'm afraid that if you're getting less than an ounce on a pull with a 10 second preinfusion, especially if a couple of drops fall in the cup, then you either have a problem with your piston mounting, or your seals, or both.

Cheers

Mike

Thanks for the further replies. I have been wondering about the seals, since I already replaced the group-boiler seal due to leakage there, and the lower sight-glass seal went on me last week. Perhaps it's time for an overhaul. OTOH, when I took the group apart they didn't look particularly worn or deformed. Can you tell whether they should be replaced from a visual inspection? And by what mechanism would the seals be causing this problem? Thanks again, all.

Joel

jrm wrote:overhaul. OTOH, when I took the group apart they didn't look particularly worn or deformed. Can you tell whether they should be replaced from a visual inspection? And by what mechanism would the seals be causing this problem? Thanks again, all.

Not necessarily. I have replaced new seals on apparantly fine looking old seals and the difference has been significant. That is because either 1) some tears/imperfections are slight and not easily visible or 2) you can get seepage between the inside of the seal and the piston shaft groove - that you cant see.

Leaky seals means some water/air escapes past the seal itself underpressure, yielding to reduced volume shots. If it is particularly leaky you might see some espresso going back into your boiler. However you should be 'feeling' less resistance in your pull too. Are you getting reasonable resistance as you pull the shot?

Up until very recently I was grinding quite fine, which required a lot of pressure (putting most of my weight behind it, feeling some flex in the lever/boiler -- probably not a good thing). I've backed off a bit now and am starting to feel a bit of slippage in the pull. I haven't really seen grounds in the boiler, but when I cleaned the piston the head had a fair bit of sludge on it. Sounds like replacing the piston seals is the way to go.

Jrm, I wonder if you may just need to adjust your pressurestat?

If it's set too low, the boiler might not be generating enough pressure to get things moving... just a thought.

Thanks for the suggestion, but this Pavoni doesn't have a pressurestat -- pressure is controlled solely by the safety valve. It may be that the spring inside the valve has stretched over time and it's now maintaining a lower pressure, but the temperatures I'm seeing at the grouphead are on the high side, which I think implies high pressure as well (?). Does anyone know if this could be the problem?

It might be, but whether there is a problem or not should be quite apparent if you see how much brew water comes out at the top of the lever pull, under normal pressure, without coffee and basket. If you are getting a good gush at good temperature then you are ok, if it is just weak/dribbly, then that would either be pressure issues or the piston head unscrewing itself from the rod. Sounds like you might be ok here though?