Water distribution systems (WDSs) are an essential part of the urban infrastructure, which consist of a labyrinth of networks of pipes, tanks, pumps and monitoring systems. In order to provide water of appropriate quantity, quality and pressure to customers, a WDS needs to be stable and reliable. Isolation valves, which are installed along the pipelines, are designed to provide system reliability. By closing related isolation valves, a pipe or a portion of the network can be isolated for inspection, maintenance and replacement without disrupting other parts of the system. However, these isolation valves may cause adverse operating conditions in the network if some of the valves in the system are active (partially or fully closed) while their statuses are unknown (due to poor or non-existent documentation, valves left closed inadvertently, errors in data transfer or valve mechanical failure, etc.). This can be observed by a disagreement between the measured pressure and flow values from the real system and results from its corresponding hydraulic simulation model. Calibration of these unknown valve statuses is, therefore, a necessary step that has to be implemented to ensure the reliability of the system. This paper introduces a hybrid method for the identification of unknown partially/fully closed valves in a water distribution network. An optimization problem is formulated for unknown valve statuses and solved by application of three sequentially applied methods, which include: a local sensitivity analysis, the application of genetic algorithms and the application of the Levenberg-Marquardt algorithm. In order to eliminate the valves that are unable to be localized by the measurement data, first, the sensitivity of the flow rates and nodal heads at measurement locations with respect to the change in the minor losses of the valves is computed. Following, a genetic algorithm combined with an extended period simulation is applied to preliminarily identify the locations of the partially/fully closed valves and their degree of opening of the valves. Finally, the application of the Levenberg- Marquardt algorithm has been implemented to correct the results from the GA model. A water distribution network is used to demonstrate the applicability of the proposed methodology. Results show that the model is able to provide relatively good approximation of the locations of unknown partially/fully closed valves as well as their corresponding settings.