1A is indeed beyond the limit of each channel of OpenSprinkler (800mA max), although I suspect this is not the source of the issue.
Here is my suggestion: in order to isolate potential problems with the valve vs. controller, just unplug the valve wire (let’s say it’s valve 6), and run a quick program, then after the program (or that valve) stops, measure the voltage between COM (or the power input bottom pin, which is internally wired to the COM pin) and station 6 port pin. Is it still 24V? If so, that’s a problem with the controller. If not, that’s most likely caused by the valve.
Technically, the way triac works is that once it’s triggered, it will continue to conduct until the zero crossing in the current (i.e. the current drops close to 0). When running on AC, there should be a zero crossing once every 1/120 second (assuming 60Hz input power). However, if due to some reason there is no zero crossing in the current, the triac will continue to conduct and will cause the valve to not close. One potential reason is if you feed DC voltage to the controller, resulting in no zero crossing in the current. But there might be other reasons.
Other than these, there are also mechanical reasons for valves to not close : for example, a lot of valves rely on sufficient water pressure to build up internally to properly close. So if the water pressure is low, or there is a mechanical issue with the valve, it won’t close. But mechanical issues are easier to tell apart from electrical issues.