A pump for pumping liquid, the pump including a drive unit and a heat sink arranged to carry off heat that is generated in the drive unit, the drive unit including a motor compartment that in the radial direction is delimited by a motor casing and that accommodates an electric motor having a stator, a coupling compartment that at least partly is delimited by a pump top casing and that accommodates a power supply component, an upper partition that is arranged between the motor compartment and the coupling compartment. The motor casing includes an outer jacket that is connected to and that in the axial direction extends between the upper partition and the heat sink, an inner stator housing that extends between the stator and the heat sink, and a gas filled gap that in the radial direction separates the outer jacket and the inner stator housing.