In a method of operating a fluid-working machine, the volume of working fluid displaced during each cycle of working chamber volume is selected taking into account the availability of other working chambers. The invention further concerns an apparatus for carrying out the method. A biasing mechanism is coupled to the housing and the cover to bias the cover to the closed position. The heat sink also has a ratio of area:thickness, as seen from a plan view, of at least 500:1 when the area and thickness are expressed in units of mm2 and mm, respectively. The insulation layer is disposed on the substrate and covers the first and second pads.