Rocket Mozzafiato R Chronometro stopped feeding water intermittently

[meatman_phr]

hello, maybe you can help, my Mozzafiato R Chronometro machine from 2021 has stopped feeding water from the E61 group. The weird thing is that it happens most of the time but not always. This means that the pump and flow are fine. Something causes the system to jam. I've taken the group apart several times and all parts seem to be in good condition and without calcification. The piston is the most suspect.

[JRising]

I don't know what piston you suspect, but I'd assume that the brew valve is probably letting the valve face separate from the brass when it's hot.