Electrolux Z355A?

I have an Electrolux Environ steam cleaner Z355A which has stopped steaming. The water is heating as normal but when I press the trigger nothing comes out. I have done the obvious- making sure its plugged in and that the safety button is unlocked. I wonder if there is some sort of blockage or loose part at the nozzle but I cant figure out how to open that part of the machine to see if this is the case. Can anyone help?