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Tanks Emptying and Won't Refill

Hello,

I have a water model where two of my tanks that 'float' on the distribution system (both have same base and overflow elevations) that will gradually empty in my EPS scenario. Neither has a separate inlet. There is a 3rd tank some distance away that is about 20' taller than the other two, thus, it should fill the two lower tanks. However, there is a PRV in between the higher and lower tanks that drops the hydraulic grade to below the lower tanks. Downstream of the PRV some distance away is a booster pump that is controlled to fill one of the lower tanks (turns ON when tank is < 80% full, and OFF when tank is > 98% full). During the EPS scenario, the two lower tanks gradually empty over time (see graph below). Furthermore, a graph of the pump shows Zero flow throughout the 72-hour simulation, although it seems to be providing sufficient head on the downstream side. There are no error/warning notifications for the pump at all. When I create a profile of the higher tank to the lower tank, the hydraulic grade shows that it is higher than the lower tanks, so i would expect the lower tanks to eventually fill up again. Demands in the system are fairly low and should not stop the tanks from filling. 

Any Insight would be appreciated. Thanks.

I am using WaterCAD CONNECT. Engine compatibility is WaterGEMS 2.00.12