Control method of a district heating grid comprising: - a thermal power plant to supply thermal power to at least one user station, - a delivery piping for hot water flowing from the power plant, - a return piping for colder water entering the power plant, - a heat exchanger in correspondence with the at least one user station having a primary branch connected to the delivery and return piping (2, 3) and to define a first closed loop with the power plant, - a valve, characterized in that the valve is placed on the first closed loop and configured to selectively close/open the inlet fluidic connection to the heat exchanger and - a by-pass duct between the delivery and return piping (2, 3) with a by-pass valve, the control method comprising the steps of: - Estimating or acquiring a demand increase time (t start - up) of power plant demand increase by the user station; - Supplying before the demand increase time (t start-up) the delivery piping based on the power demand of the power plant with hot water when the by-pass valve and the valve are switched so as to define a second closed loop through which the water flows, the second closed loop substantially excluding the exchanger and including the return piping so that the flow rate at the temperature (T delivery) flows through the by-pass duct towards the return piping, with a consequent preheating of said second closed circuit and increase in the water temperature received by the at least one power station; - Switching, based on the power demand of the power plant, the valve and the by-pass valve so that the hot water of the delivery piping flows through the first closed circuit including the heat exchanger and the return piping, and the temperature (T delivery) downstream of the by-pass duct is higher than that of when the step of supplying began. - a thermal power plant to supply thermal power to at least one user station, - a delivery piping for hot water flowing from the power plant, - a return piping for colder water entering the power plant, - a heat exchanger in correspondence with the at least one user station having a primary branch connected to the delivery and return piping (2, 3) and to define a first closed loop with the power plant, - a valve, characterized in that the valve is placed on the first closed loop and configured to selectively close/open the inlet fluidic connection to the heat exchanger and - a by-pass duct between the delivery and return piping (2, 3) with a by-pass valve, the control method comprising the steps of: - Estimating or acquiring a demand increase time (t start - up) of power plant demand increase by the user station; - Supplying before the demand increase time (t start-up) the delivery piping based on the power demand of the power plant with hot water when the by-pass valve and the valve are switched so as to define a second closed loop through which the water flows, the second closed loop substantially excluding the exchanger and including the return piping so that the flow rate at the temperature (T delivery) flows through the by-pass duct towards the return piping, with a consequent preheating of said second closed circuit and increase in the water temperature received by the at least one power station; - Switching, based on the power demand of the power plant, the valve and the by-pass valve so that the hot water of the delivery piping flows through the first closed circuit including the heat exchanger and the return piping, and the temperature (T delivery) downstream of the by-pass duct is higher than that of when the step of supplying began. - Estimating or acquiring a demand increase time (t start - up) of power plant demand increase by the user station; - Supplying before the demand increase time (t start-up) the delivery piping based on the power demand of the power plant with hot water when the by-pass valve and the valve are switched so as to define a second closed loop through which the water flows, the second closed loop substantially excluding the exchanger and including the return piping so that the flow rate at the temperature (T delivery) flows through the by-pass duct towards the return piping, with a consequent preheating of said second closed circuit and increase in the water temperature received by the at least one power station; - Switching, based on the power demand of the power plant, the valve and the by-pass valve so that the hot water of the delivery piping flows through the first closed circuit including the heat exchanger and the return piping, and the temperature (T delivery) downstream of the by-pass duct is higher than that of when the step of supplying began.