I have had the flow control plug several times. Have a baggie and a rubber band to stop the flow out of the regulator when you screw the flow valve out of the tank. As you unscrew the valve out, cover the end of the line with the baggie. Clean the holes out with air and reassemble the unit. It will work as soon as oil starts to circulate.
It seams to plug on me when the lines as frozen solid for several days.
Daryl