A device for producing hot fluid, in particular domestic hot water, comprising: - a tank for receiving liquid, equipped with at least one fluid inlet and one fluid outlet, at least the part of the tank called the inner part, suitable for being in contact with the liquid filling the tank, being made of synthetic material, - a system for heating the contents of the tank, - a heat exchanger comprising a primary circuit equipped at least with a fluid inlet and a fluid outlet, a secondary circuit equipped at least with a fluid inlet and a fluid outlet, and a zone, for heat exchange between the primary and secondary circuits, which is arranged outside the tank, - a loop circulation circuit between the tank and the primary circuit of the heat exchanger, and - a pump arranged on the loop circulation circuit, the inlet of the secondary circuit of the heat exchanger being connectable at least to a source of fluid to be heated, in order to allow the production of hot fluid at the outlet of the secondary circuit, - a valve arranged on the loop circulation circuit between the tank and the primary circuit of the heat exchanger, - a drive member for moving the valve between an open position and a closed position, - a unit for controlling at least the pump and the drive member for moving the valve, the control unit being configured to control the actuation of the drive member for moving the valve and thus the passage of the valve from the open position to the closed position, or vice versa, depending on the on/off state of the pump, characterized in that the tank comprises, in the lower half of the tank, on the outer surface of the tank, a reservation inside which the heat exchanger, which is a counter-current exchanger, preferably with plates, is able to be housed in order to extend at least partially within the overall contour of the tank. - a tank for receiving liquid, equipped with at least one fluid inlet and one fluid outlet, at least the part of the tank called the inner part, suitable for being in contact with the liquid filling the tank, being made of synthetic material, - a system for heating the contents of the tank, - a heat exchanger comprising a primary circuit equipped at least with a fluid inlet and a fluid outlet, a secondary circuit equipped at least with a fluid inlet and a fluid outlet, and a zone, for heat exchange between the primary and secondary circuits, which is arranged outside the tank, - a loop circulation circuit between the tank and the primary circuit of the heat exchanger, and - a pump arranged on the loop circulation circuit, the inlet of the secondary circuit of the heat exchanger being connectable at least to a source of fluid to be heated, in order to allow the production of hot fluid at the outlet of the secondary circuit, - a valve arranged on the loop circulation circuit between the tank and the primary circuit of the heat exchanger, - a drive member for moving the valve between an open position and a closed position, - a unit for controlling at least the pump and the drive member for moving the valve, the control unit being configured to control the actuation of the drive member for moving the valve and thus the passage of the valve from the open position to the closed position, or vice versa, depending on the on/off state of the pump, characterized in that the tank comprises, in the lower half of the tank, on the outer surface of the tank, a reservation inside which the heat exchanger, which is a counter-current exchanger, preferably with plates, is able to be housed in order to extend at least partially within the overall contour of the tank.