Fluidized bed combustion is suitable for the combustion of various fuels, including low-reactivity materials, due to the intense mass and heat transfer in the combustion zone. However, low ash melting points can lead to operational issues, ranging from sticky deposits on heat transfer surfaces to bed defluidization. The aim of this work is to develop a method for determining the agglomeration tendency of bed ash. For this purpose, bed ash samples, which were collected over a longer period from a stationary fluidized bed combustion system, are analyzed regarding their particle size distribution, chemical composition and ash melting behaviour, compared with the input bed material. The results of the particle size analysis show, that the effect of abrasion outweighs the effect of coating and agglomeration formation. Furthermore, it is determined, that due to the identified chemical composition and the softening temperatures of the bed ash samples, agglomeration in the bed should not occur. In practice, agglomeration still occurs, which can be attributed to the following three main causes: Firstly, the coatings may exhibit softening temperatures due to their chemical composition which are below the typical average bed temperature during coating-induced agglomeration. Secondly, local temperature increases (hotspots) can occur in the bed. Thirdly, the coating layers of the bed ash particles could not be analyzed separately. Therefore, the determined proportions of Na2O, K2O, CaO, MgO, Al2O3 and SiO2 represent the bulk composition or the averaged composition of the entire particles. However, the coating layer has a lower SiO¿ content and consequently a higher proportion of the other components, which leads to a lower melting point.