... whatever it is, this machine has never been open.
Then this was an eye-opening as well as a machine-opening experience for you! Ever since my Aggie days, as soon as I get anything I start tearing it apart to see what makes it tick & how it can be improved.
There are no pstats in Gaggia's. The self-priming-valve (SPV) is Gaggia's miscarried attempt to dumb down some of their machines. They figured the typical noob wouldn't be able to figure out how to prime a boiler so they came up with this brain-fart.
Supposedly, it permits air to escape from the boiler during startup, preventing air locks. Then, once the boiler is full, a pea-valve is supposed to close, stopping hot water & steam from venting into the water reservoir. Guess what?
THEY DON"T WORK! I once had a handful of new Carezza's that a friend bought as Christmas gifts for selected employees. He asked me to check them out and install PID's & OPV's. While testing I left each machine on & idle for a couple of hours, and the water in each machine's reservoir reached ~160?F. I was concerned because the Ulka pumps have a maximum temp rating of 50?C - I saw the possibility of premature pump failure at these temps.
When I asked Gaggia about it they replied that it was a tried & tested design and that they were happy with it. That's when I decided to come up with a mod to correct the problem myself. The file I attached to an earlier post was the result of that effort, and I'm happy to report that it's become one of the most common mods made to Gaggia home espresso machines.