Abstract: A continuously operated boiler heated with a pressurized circulating fluidized bed firing consists of a fluidized bed burner chamber (1) and one or more cyclones (5) connected in series after the fluidized bed burner chamber (1) and on the flue gas side. A fluidized bed cooler (12) is connected in series after each cyclone (5) which cooler is connected by way of a dip pot (8) with the solids output of the cyclone on one hand and with the fluidized bed burner chamber 91) on the other hand. A return conduit (10) is connected with the dip pot (8) which opens into the fluidized bed burner chamber 91). Pressure vessels (18, 19) house the fluidized bed burner chamber (1), the cyclone (5) and the fluidized bed cooler 912). The fluidized bed cooler (12), the cyclone (5) and the dip pot (8) are thereby combined into a unite which is housed in the common pressure vessel (19).