Detecting and localizing faults in building systems like heating or cooling is essential to reduce energy consumption. Hence, there is a need for innovative diagnosis applications. In this paper, we report on an initial study to show the potential of model-based diagnosis in the building domain. We present a model for heating systems and discuss the results of the obtained diagnosis, considering the expected behavior of different case studies. The approach provided reasonable diagnoses depending on available observations. In addition, the same component models can be easily re-used without adaptations. Hence, applying model-based diagnosis for building systems is a feasible alternative to other approaches.