Reliability become one of the main things in industrial world. Power plant is one of industry that need pay attention in reliability. One of Power plant in Java Island is Combined Gas and Steam Power Plant Gresik. There is lots of support equipment in Combined Gas and Steam Power Plant, one of them is Control valve Level Steam Drum Heat Recovery Steam Generator (HRSG). This Control Valve is one of tool that use as level regulator Steam Drum HRSG. When there is disturbance to control valve, can interfere with production of steam which will also affect the MW power generated by steam turbine itself. In last 2 years, disturbance in control valve and its supporting component increased, caused the performance of Combined Gas and Steam Power Plant Gresik itself disrupted. Nonlinear programing can be used as one of the method to reduce breakdown and increase reliability with preventive maintenance.

Keywords : Nonlinear Programing, Control Valve, Hazard Rate, Preventive maintenance, Reliability.