Abstract: A solar collector having a radiation absorber (1) has a number of channels for conducting heat receiving liquid, said channels accommodating particles for capillary effect to lift the liquid to effectively sweep the sun-facing surface layer of the absorber. The solar collector is started after a prolonged operation standstill by driving a liquid pump (7) intermittently by a control unit (13) acting according to a clock-controlled program. In the intermittent start-up phase, first the pump (7) is driven for 2-4 minutes, thereafter it is shut down for a time span of about 20-60 seconds, and this is repeated two or three times before a continuous operation phase is started. Thereby air in the absorber (1) channels is expelled more rapidly.