An oven includes a cooking chamber for housing food to be cooked, a control unit, and a reservoir for containing washing detergent at room temperature. The washing detergent has an activation temperature. The oven also includes a liquid supply arrangement selectively activated by the control unit for supplying the washing detergent into the cooking chamber, and one liquid heating element for heating the washing detergent and to be selectively activated by the control unit. During a washing cycle, the control unit performs the following ordered operations: a) activate the one liquid heating element for a first time period sufficient to increase its temperature to the activation temperature; b) deactivate the liquid heating element; c) when the temperature of the liquid heating element is about the activation temperature, activate the liquid supply arrangement so that the washing detergent is heated by the liquid heating element while supplied into the cooking chamber.