DE 4317554 A UPAB: 19950117 In addition to the liq. fuel inlet (8) the boiler has several fresh air inlets (41,46) and a water inlet (2). There are several combustion stages (16,20) with catalytic combustion chambers, surrounded by water chamber (4), at least partly. The fuel air mist flows through the combustion stages. There is a flue gas heat exchanger for the heated water, supplied from the combustion chambers. The first combustion stage (16) has an evaporator chamber (40), which has on its edge (31) outside a catalyst layer (13). ADVANTAGE - Provides a facility for liquid fuel use without cracking.