The aim of the present work is to contribute to the analysis of parametric sensitivity in fixed bed reactors using an heterogeneous two dimensional model. The sensitivity functions are calculated along with the state variables and the bound of the region of parametric sensitivity is drawn by the maximum of the sensitivity of the particle temperature at the hot spot. The results show that with a two dimensional heterogeneous model runaway risk can be detected for operating conditions the one dimensional model qualifies as stable. This method can be applied to any reaction scheme, simple or complex. The runaway limit proved to be coincident whichever the parameter in question allowing to centre the analysis on simple operating parameters such as inlet gas concentration or temperature which are easily manipulated. In addition it highlighted the influence of the coolant temperature upon reactor stability and showed to be in good agreement with other criteria to foresee runaway.