The autofill valve of my Vesuvius, the one placed in the big brass piece under the group, was replaced when the machine was serviced. All this big part was replaced but the pressure sensor. Despite this the one way valve returned water from the brew boiler to the water tank after replacing it. Fortunately, a few weeks later, it started to work properly, no more water escaping to the tank. Unfortunately, the pressure behaviour we are talking about was never gone.
If the service boiler was overfilled, you wouldn’t have proper steam, just a lot of water if I’m right ¿?
I think we’d have to focus on the first stage of the profile, it’s during the preinfussion where the machine has trouble, this small stop around the 1,5 bars mark. Overshooting is just a consequence of this. As @AlJuar points, the fail is more prone to occur when the machine has been idle, cold, for a long time. It seems to be worst when weather is cold. That’s why I thing it’s a mechanical issue. But yes… it’s very very difficult to solve this far from a machine.
