Heating method and device of water heater

The invention provides a heating method and device for a water heater, and the method comprises the steps: detecting the initial temperature of liquid in a hot water tank, controlling the liquid to circularly flow in a cooling pipeline when the initial temperature is greater than or equal to a first preset temperature, detecting the cooling pipe liquid temperature of the liquid in the cooling pipeline, and controlling the liquid to circularly flow in the cooling pipeline when the cooling pipe liquid temperature is equal to a preset water outlet temperature; and when the preset triggering condition is met, liquid in the cooling pipeline is controlled to flow out. The liquid in the hot water tank is heated in advance, and due to the fact that the temperature of the liquid in the hot water tank is high, the water outlet temperature can be more rapidly tended to the preset water outlet temperature through heat exchange, and the water outlet waiting time of a user is shortened. Wherein the preset water outlet temp