Hi Sharron,
I'm no engineer but I had the same issue with my steam generator. It happened to be a faulty switch in the handle.
If you are able to, unscrew the handle and remove the switch - it's dead easy to do. Take it to your local maplin who should have them in stock. The Maplin switch costs about £1.50 as opposed to £25+ just to take a look at the iron by a specialist. I've had no bother with it since and it works beautifully.
Hope this helps
kanak, July 2011