This paper highlights the importance of modeling correctly the operational constraints of Combined-Cycle Gas Turbines in a unit-commitment-type framework. In practise in Colombia, when given an initial dispatch by the Independent System Operator, Combined-Cycle Gas Turbine plants are operated according to the results of a heuristic simulation code. Such heuristics omit technical operating constraints such as: hot, warm or cold startup ramps; minimum hours required of gas turbine to start a steam turbine; relation between dispatched number of steam and gas turbines, load distribution between gas turbines, additional fires etc. Most unit commitment models in the literature just represent standard technical constraints like startup, shut down, up/down ramps and some of them even additional fires. However, they disregard other real-life CCGT operating constraints that are considered in this work. These constraints are important because they ensure avoiding equipment damage that can potentially put the Combined-Cycle Gas Turbine out of service, and ultimately lead to lower operating costs.