Arrangement for circulating liquid in a liquid cooler (11) intended particularly for power electronics appliances, inside which cooler at least two longitudinal main ducts (22, 23) are arranged and transverse ducts (21) arranged between them and connecting them, and in which cooler at least one of the longitudinal ducts is an input duct (22), into which liquid from coming from outside is led via an input joint (12) and one is an output duct (23), from where the liquid is led out via the output joint (13), inside which output duct a tubular additional part (41) having an open end at least on the side of the output joint is installed, and which additional part is arranged detached from the output duct such that a gap remains between the outer surface of the additional part and the inner surface of the output duct for enabling a liquid flow in the output duct outside the additional part, and in which arrangement a first aperture or first apertures (P, N, P2) are arranged in the part of the additional part on the output joint side and/or in the output joint and/or between them for enabling a first path of passage for a part of the nominal total flow to the output joint, and a second aperture or second apertures (T, P1) are arranged in the part of the additional part that is farther from the output joint or between the additional part and the output duct for enabling a second path of passage for the remaining part of the total flow into the additional part and via it onwards to the output joint.