Hugonl37 I think there is something that gets stuck in the pressure circuit - probably the one-way valve actuated by the solenoid identified by the arrow.
It may ‘float’ in and get stuck, so the valve doesn’t close fully, and the pressure causes flow-back into the pump and the tank, then the ‘something’ is dislodged, but doesn’t go far, and the valve closes properly for a while.
I would wait for the machine to ‘cause trouble’ again, so you are reasonably sure the piece of whatever-it-is is in the valve, then shut the machine down, let it cool, empty the brew boiler (so any leak is ‘contained’) and take apart the valve, removing it from the pressostat and the pipe to the brew boiler (and disconnecting the flex tube to the pump - all compression fittings), then open and clean. I don’t know if ACS would advise replacing any gaskets, or whether they may be replaced by liquid sealant. The pipe joints are easy to seal with PTFE.
