I had the same problem. I found the trigger button at SmallAppliances.com. You'll have to pry off the rubber grip, and unscrew one or two screws on the handle, bu the trigger inserts neatly into the space. Screw it back together, snap on the rubber grip and it will work like new. Below is the part number & price.
Rowenta DG0123 Knob Trigger, Blue $9.99 (plus shipping)
Watch out, the next thing that will go is the on/off switch. Once it starts getting difficult to turn the unit on or off, just plug and unplug it until you get the new part, or you will be stuck one day and need the iron and go to turn it on and it wont start.
The part is $20, and the same site has it available.
Michael, February 2009
