Why does my Philips 8300 series steam generatorcut out once it reaches stea?

The steam generator process heats up, the green light flashes to indicate working to get to temperature, the red/organge light on the heel of the iron is glowing brightly, there is water in the reservoir and then ....... the iron reaches steaming temperature, audibly clicks off and the light on the heel of the iron turns itself off.

But WHY??????????????????????????????