The first thing is to check whether this is a problem with the valve, or circuit problem on OpenSprinkler. The easiest is to switch that zone wire to a different zone port and test that zone, see if the valve functions correctly. If so, it’s likely that the triac (AC transistor) on the original zone has gone bad and needs to be replaced. If switching to a separate zone, the valve still doesn’t work, it’s likely a problem with the valve.
Problems with valves can also have a few different possibilities: mechanical or electrical. I don’t know much about mechanical problems, but in terms of electrical problems, you can test the resistance between the COM (common) wire with that zone wire. The resistance should be between 20 to 50 ohm. If it’s too small, there is likely a shorting somewhere. If it’s too large, may be a broken wire.