A dual-wall, vacuum-insulated container (30, 40) has an external wall (1), an internal wall (3) and there in-between a vacuum chamber (5), in which there is arranged a heat insulation device (2, 20). At least three temperature sensors (13, 13a, 13b, 14, 15) that are spaced apart from another recurringly register instantaneous temperatures (T1, T2, T2A, T2B, T3) of the container (30, 40). At least in some points there is calculated a temperature course using a heat insulation model on the basis of the construction and material characteristics of the container and the heat radiation resulting therefrom, which temperature course contains at least two of the temperatures (T1, T2, T2A, T2B, T3) registered. From the temperature course there is calculated a desired temperature value for the position of at least one further of the temperature sensors and compared with the actual temperature value actually registered by this temperature sensor. From the deviation between the desired temperature value and the actual temperature value there is detected a change of the heat insulation quality of the container.