I'm trying to track down why my sprinkler valve stopped working. For a while it was surging (sprinkler heads popping up and down like there wasn't enough pressure) and then they stopped working entirely.

The controller is working and the solenoid is getting power. I don't think it's the solenoid because I tried swapping solenoids with the other valve right next to it and it still wouldn't work, yet the other valve works with either solenoid in it.

I can turn the small black plastic screw on top (bypass?) and then the water starts flowing fine to the sprinklers, but water sprays out of the screw so that's not even a manual solution.

My first guess is that dirt has clogged some passage in the valve, but I took the valve apart and didn't see anything in there. I cleaned and put it back together, but still no luck.

Thanks in advance for any thoughts on what to check next.