If the unit isn't turning off automatically
With the water to the unit turned on, open up the valve after the unit (the one producing pure water), then tilt the main unit at a 45 degree angle and hold it for 20 seconds. Lower it back to level, and then lift up the opposite side and hold it at a 45 degree angle and wait 20 seconds to lower it back to level (or normal) position. This should purge any trapped air bubbles in the system and auto shutoff valve (ASOV). With it back in place, close the valve again and see if it shuts off after 15 - 60 seconds.