problem with outdoor pipes

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Hello, I´m trying to simulate a radiant wall connected to a boiler system for heating water. In the experimental framework, we have connected the elements through pipes (under outdoor conditions) which present heat losses. When I include the element Pipe:Outdoor in the Plant circuit, the Radiant System and the Boiler don´t operate. This failure occurs only when hot water flows by the circuit. Does it have a solution? Thanks!