Just want to put in some keywords that would have been helpful to me when diagnosing the issue with my Rancilio Silvia. My machine would make a loud gurgling (boiling bubbling) sound every time the boiler cycled, and return hot water to the tank through the discharge tube. Eventually the water in the tank would heat up and the boiler would be drawing in hot water. I didn't have issues for the first couple hours the machine was on, but eventually the OPV would relieve so much pressure I couldn't pull a shot properly, it would just stop flowing with the filter basket in place. I could remove it, run water through the grouphead, and then continue pulling the shot, but it was basically unusable.
The repair was simple, I followed along with this guy https://www.youtube.com/watch?v=_LE0Di7nG5Y and it worked well. Getting the nuts to loosen required a lot of leverage and a bigger wrench than expected. I didn't disconnect the wiring to the switches, but I would next time as I bashed into them when the tension on the nut let go. It wasn't obvious but turn both of them left to loosen. Then a quick clean of the parts, added the 3 pieces from this kit and reassembled. Take a reference photo of the spacing between the two nuts before you disassemble anything. I don't have a pressure gauge, but the linked video suggests that 130 g of water in 30 seconds through the discharge hose with a blank filter in corresponds to 9 bars. I ended up with 108 g of water, so probably 10 or 11 bars, and I'm happy with the results.
This was a good buy, much cheaper that bringing the machine in for servicing and being without it for 6 weeks. The repair took a total of 15 minutes, I'd definitely do this again.
