For complex systems (e.g. with many pipes and a lot of controls) it can take more than the standard 40 iterations to converge on a good solution. In cases like this, sometimes increasing the number of Trials in the Calculation Options will allow the model to converge to a good solution. However we often find that models that give the ‘unbalanced network’ error have data entry errors (high friction coefficient, etc.) so it is always a good idea to check your data input carefully."