Why would my Steam Tek cleaner make a humming noise and produce no steam?

My Steam Tek Floor cleaner,I have taken it apart because it was not making steam and making a noise which i found to be what i believe is the pump.after examination when the unit is turned on water flows freely from the reservoir right thru to the flooer unit so there is no blockage,Is the water supposed to be held in the steam chamber alllowing it time to heat up,is ther a valve or somthing in the steam chamber that could be malfuntioning.Can someone please explain to me how this unit is supposed to work,from reservoir to floor pad.Thanks