radially on a portion of the pipe 36 which is between the bottom thereof and a portion corresponding to below the plates 42 whereas the holes 96 are only provided on a portion of the pipe 36 which faces towards the cyclone device 18 through the passage 32 the second outlet 90 is connected through the pipe 98 to the pipe 70 of the fire grate 66 both the first outlet 88 and the second outlet 90 are controlled to be opened and closed by means of conventional valve means 100 and 102 respectively as illustrated in fig1 and 3 an indicator tank 104 containing a floating member 106 therein is secured between the hot water tank 74 and air chamber 86 on the casing 12 the indicator tank 104 is in communication with the space within the hermetic casing 12 through a pipe 108 so that the floating member 106 floats up and down corresponding to the water level within the space in the casing 12 the floating member 106 is operatively connected for example electrically with a valve 110 which is mounted on the water supplying pipe 22 a signal created by the floating member 106 can be.