Ford Galaxy overheating?

I have a 2006 Ford Galaxy & I have a problem with it overheating, at first my Ford dealer just flushed the system ( broke down within a few days) , then they replaced the thermostat ( the car was then ok for 4 months) then the issues came back, temperature gauge goes from mid to red in seconds , loss of power & then cuts out- this time they replaced the Thermostat, Water pump , Injectors & Head Gasket , this seemed to resolve the problem for 10 days & then Sat night it overheated again - any ideas ?