Well, this issue's got me stumped.
I've been using Creminas 73 and 2011 models for 12 years and before that my 1980 Europiccola for 10 years and never has this issue occurred or been mentioned in the forums to my knowledge. It relates to the 2011 Cremina, which I've been using for the past 6 years.
Basically, for the past 6 months every few shots, so intermittently, the lever has no pressure when pressed down pulling a shot; this despite the pressure gauge reading .8 bar (and the fact that I have already run water through the group and it seems to gush out normally). What happens is that after lifting the lever and holding for 15 seconds I push down and there is little resistance and no water/coffee comes out. Them I pump the lever a few times until I feel it 'bite' and eventually a long thin watery shot comes out. These shots always look and taste terrible and always result in a watery puck and residual pressure left over at the portafilter when I release it; viz. portafilter 'sneeze'
In other words, the lever every once and while simply doesn't 'bite' when pushed down. There is no resistance. So what I have tried to rectify this?
My first thought was scale was blocking the inlet hole in the group thus preventing water from coming out. And yes the machine did need a big descale which I performed carefully and thoroughly. Now the water really gushes out when the lever is raised with no portafilter or an empty portafilter, but the abovementioned problem still remains. I used proper descaling solution, not citric, so the actual scale is dissolved so it can't still be there potentially blocking the inlet hole or even the feeder tube from boiler to group. (More on the 'feeder tube' below).
Next I serviced the group and piston gaskets, checked and re-lubed everything. I do this every 3 months anyway because I find the group needs constant lubing and maintenance to run smoothly. The issue is often worse after re-lubing (using Dow 111) which makes me think maybe lube is blocking the inlet hole (not that I put much on, and not that this has ever occurred before in any of the machines I've used over the past years).
Now I'm thinking either the problem has something to do with 'pressure', a 'blocked feeder tube' or damaged/faulty portafilter gasket.
Re the pressure issue, I can't think what it may be. The Mater pressurestat works fine. I can check it with another gauge I can put on the boiler cap which I use with my 73 Cremina. So could it be the internal pressure relief valve. Normally problems here are evidenced by a leak, and there is no leak, or hissing in the machine.
Or is the issue connected with a blocked feeder tube? The tube in the post 2011 Creminas are internal, attached to the boiler and not the group itself (as with the 67 Creminas). So how the hell do I descale or otherwise unblock this tube? I've used descaler to the point that anything in there should have been dissolved and anyway, as I've said, water gushes out when not pulling a shot, so I doubt this is the issue.
And finally, the portafilter gasket. This gasket is the worst thing about the the new Creminas (never an issue with the 67 Creminas). They are a real bugger to put in and can easily get damaged. I gave up long ago with the red OEM gaskets and use either black OEM gaskets from Migg Frei or the old black ones from OE which they don't make anymore. I know when this gasket is faulty or damaged because it leaks. But maybe it is faulty, and while not leaking is still somehow letting air in. I don't know. Just an idea, but given the nature of the sharp edges on the group and the hassles installing these gaskets this could be the source of the issue.
So all up, any ideas? Apologies for the long post and thanks to those who have got this far. Is anyone able and/or willing to tell me whether I've missed anything, because surely this annoying problem is solvable?