An infusion pump device (10) comprises a primary reservoir (11) for liquid medicament, a pump (14, 16) with a secondary reservoir (14) that is able to retrieve liquid medicament from the primary reservoir and to subsequently dosing said liquid medicament from the secondary reservoir in incremental steps, a first upstream conduit (24) fluidly connecting the primary reservoir with the pump, a second downstream conduit (25, 28) fluidly connected to the pump for transporting the liquid medicament to an infusion site interface (30), a valve (35) for alternatingly connecting the pump to one of the two conduits, and a control unit configured to control the operation of the infusion pump device. For filling the fluidic system (24, 13, 25, 28) of the infusion pump device with liquid medicament prior to infusion operation, the control unit causes the infusion pump device to carry out the following steps: (a) bringing the pump to an initial state where an inner volume (13) of the secondary reservoir is minimal； (b) switching the valve to a first state, in which the secondary reservoir is connected to the first conduit and the primary reservoir； (c) retrieving liquid medicament from the primary reservoir, wherein the retrieved liquid volume (V c ) is at least equal to the inner volume (V B ) of the first upstream conduit； (d) switching the valve to a second state, in which the secondary reservoir is connected to the second downstream conduit； (e) expelling the contents in the secondary reservoir into the second downstream conduit； (f) switching the valve to the first state； (g) retrieving liquid medicament from the primary reservoir, wherein the retrieved liquid volume (V c ) is at least equal to the inner volume (V D + V E + V F ) of the second downstream conduit； (h) switching the valve to the second state； and (i) expelling the contents in the secondary reservoir into the second downstream conduit by shifting the piston to the initial position.
