A pump (2) system includes a pump, a sensor (22; 28) arranged in or at a flow path (14), and a concentration measurement device measuring a concentration in liquid inside the flow path (14). The concentration measurement device includes the sensor (22; 28), as a concentration sensor, connected to an evaluation device (26) for evaluating readings of the sensor (22; 28). The evaluation device (26) is connected to a further signal source (20; 24), providing at least one further parameter, and is configured to carry out an evaluation of the reading of the sensor (22; 28), taking into account the further parameter provided by the further signal source (20, 24) to output the concentration in the liquid. A solar heating system includes the pump system.