A fluid ejection device controller for controlling a fluid ejection device of a three dimensional printing system has a processor and a memory. The memory includes executable instructions that when executed by the processor causes the fluid ejection device controller to control a motion of the fluid ejection device to print agent onto a layer of build material in a build area; and to flush agent through at least one nozzle of the fluid ejection device in response to detecting, by the fluid ejection device controller, an erroneous stopping of the motion of the fluid ejection device and the fluid ejection device being positioned on top of the build area.