Most zone valves have a manual override...it should be safe to open it. The valve could be open, and not circulating in that loop because of an air lock, though, and purging might solve the problem...the valve could be okay. But, I think I'd try to manually open it to see if that does anything before I tried to purge it.
Depending on the brand and type, it might just be the motor head, which is replaceable without changing the valve.
To purge, the valve would have to be open, either manually, or, it's possible it is already open if the thermostat is calling for heat, but not flowing because of an airlock. Some have an indicator that shows whether it is closed or open.