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A photoionized gas under constant pressure can display thermal instability with three or more solutions for possible thermal equilibrium. A unique solution of the structure of the irradiated medium is obtained only if electron conduction is considered. The subject of our study is to estimate how the efect of thermal conduction affects the structure and transmitted spectrum of the warm absorber, computed by solving radiative transfer with the code titan. We developed a new computational mode for the code titan to obtain several solutions for a given external conditions and we test a posteriori which solution is the closest one to the required integral condition based on conduction. We demonstrate that the automatic mode of the code titan provides the solution to the radiative transfer, that is generally consistent with the estimated exact solution within a few per cent accuracy, with larger errors for some line intensities (up to 20 per cent) for iron lines in an intermediate ionization state.