Water heater stratified horizontal cylinder shape

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Hi, I am simulating two solar water heating systems with a storage tank stratified. One with vertical shape and the other with horizontal shapes. Happens that when I try to simulate with horizontal shape, the output StorageTank Use Side Outlet Node has constant values, the same of the setpoint temperature. The same doesnt happen with the vertical tank. And in both systems, the heater capacity is 0, because I'm using a instantaneous water heater (Water heater mixed). So, does anybody has an idea of what is happenning?