COMBUSTION CONTROLLER

PURPOSE:To avoid explosion sound caused by a residual unburned gas and discharge hot water in the early stage by providing a rotational speed detection means for the rotational speed of a fan and a suppression means which suppresses prepurge action when the detected rotational speed is in excess of a special rotational speed which is set lower than a lowest rotational speed in driving. CONSTITUTION:When starting discharge of the hot water,, it is judged by a water flow sensor 1 whether the rotational speed of a fan 7 is over a specified rotational speed. If it is over the specified speed, a gas for combustion is supplied from a combustion circuit 9 without prepurging action and at the same time the combustion gas is fired by an ignitor 15 and the fan 7 is rotated at a specified speed to supply the air for combustion in order to obtain a specified air-fuel ratio. When it is judged that the rotational speed of the fan 7 has not reached a special rotational speed, the prepurge action performed is, and after the prepurge is finished, the rotational speed of the fan 7 is shifted. Accordingly the fan 7 is rotating by its inertia and if its speed is over a special speed which is enough to exhaust the unburned gas, the prepurge is not made and the combustion is started at once to reach early a specified temperature in the hot water.