This investigation presents a comprehensive evaluation of an actual combined power plant in Barranquilla, Colombia, to quantify the energy losses. Data from two test campaigns were analysed to assess operational conditions and identify turbines inefficiencies. The original design of the combined power plant aimed to generate over 450000 kWh, but measurements showed a significant decrease of 3098 kWh, impacting the reliability charge of the plant. Results indicated that the plant performance varied between official tests, from 49.11% to 48.5%. The vapour turbine block was found to experience a power capacity reduction of 5240 kWh, while the gas turbine block saw an increase of approximately 2142 kWh. The evaluation showed that the relative electrical efficiency of the vapour turbine block decreased from 90.25% to 88.39%. In consequence, inefficiencies in the medium-pressure and low-pressure turbines accounted for 65.9% of the energy drop, while operational changes contributed 34.1%. The operational changes were identified between the inlet an outlet vapour turbine stage. Furthermore, it is crucial to inspect potential losses in moving crowns and losses resulting from clearance between the rotor and stage guides, as these factors may elucidate the decrease in the efficiency of the vapour turbines.