So I had my Breville Barista 870 for over 7 years now. Cleaned and descaled regularly (first 3-4 years with 50/50 vinegar then with DEZCAL solution). It started buzzing after couple years which indicated possible solenoid problem, but the pressure was good, consistent shots and steam was fine.
Now fast forwarding to this month, everything was working, I descaled machine beginning of September, made first latte next day no problem, then later in the day I tried to do the same, espresso was fine, but the steam would not go as usual. It was giving some steam, not barely any pressure. It was also showing some steam through the group head, I removed portafilter and got lots of steam from there. Then switched to hot water dispenser and similar results - hot water coming through group head and a little through hot water nozzle.
This make me think there's something wrong with solenoid and it doesn't close valve that stops water from going to the group head. I disassembled the machine and there are no leaks and looks fine.
I just want to confirm that I'm right and replacing the solenoid assembly will fix the issue. Any other possible solutions? Could I replace just one of the solenoids? Would it be the 3-way? How would I test the solenoid to see if it's broken?
Thanks!

Disassembled the 3-way solenoid valve and found the problem. The compression spring inside it snapped

Solved it by buying a similar spring at hardware store, stretching a bit on one side and cutting it to size.
It works, but buzzing is still there and it feels louder.
Might be because spring tension is different or might be a faulty solenoid in general. The pressure is fine though and steaming normally.