Control device for a hot water system having a thermal store; - having an interface, a controller and a data memory; - the controller being connected to the interface and the data memory, - the interface being connectable to a temperature sensor of the thermal store and being designed to measure a temperature signal from the temperature sensor which correlates with a temperature of a thermal storage medium that can be arranged in the thermal store and to provide the said signal to the controller, - a predefined threshold value being stored in the data memory, - the controller being designed to assign a measurement time (t) to the acquired temperature, - the controller being designed to determine a change (dT/dt) in the temperature over the measurement time (t), - the controller being designed to compare the determined change (dT/dt) with a predefined threshold value in a comparison, - the controller being designed to define a control parameter in the data memory to control a heat source of the hot water system on the basis of a result of the comparison, - characterized in that - wherein the interface can be connected to a circulation pump, - wherein the controller is designed to detect an operation of the circulation pump, - wherein the controller is designed to check an operating state of the circulation pump at the respectively associated measurement time (t), - wherein the controller is designed to ignore the result of the comparison when there is an active operating state of the circulation pump at the measurement time (t) and when the change (dT/dt) in the temperature falls below the predefined threshold value. - having an interface, a controller and a data memory; - the controller being connected to the interface and the data memory, - the interface being connectable to a temperature sensor of the thermal store and being designed to measure a temperature signal from the temperature sensor which correlates with a temperature of a thermal storage medium that can be arranged in the thermal store and to provide the said signal to the controller, - a predefined threshold value being stored in the data memory, - the controller being designed to assign a measurement time (t) to the acquired temperature, - the controller being designed to determine a change (dT/dt) in the temperature over the measurement time (t), - the controller being designed to compare the determined change (dT/dt) with a predefined threshold value in a comparison, - the controller being designed to define a control parameter in the data memory to control a heat source of the hot water system on the basis of a result of the comparison, - characterized in that - wherein the interface can be connected to a circulation pump, - wherein the controller is designed to detect an operation of the circulation pump, - wherein the controller is designed to check an operating state of the circulation pump at the respectively associated measurement time (t), - wherein the controller is designed to ignore the result of the comparison when there is an active operating state of the circulation pump at the measurement time (t) and when the change (dT/dt) in the temperature falls below the predefined threshold value.