Did you already submit a support ticket? I just responded to one that’s similar to this, and turns out the issue is due to the RPi operating system. I recommend you to try our pre-configured SD card image and see if that works. If you have an existing RPi system and install OpenSprinkler firmware on top of it, make sure there is no other program that interferes with GPIO operations.
Also, check the valve you have: OSPi is only compatible with 24VAC sprinkler valves. It’s not compatible with DC valves or latching solenoid valves (which typically have very low resistance, like <10 ohm).