On some irons where you you have a fill cap on a short length of nylon cord, this cap or stopper has a small breather hole that can become blocked. Use a small needle or paper clip and push that through the hole to clear any obstacle.
The easy way to find out if it is the cap is to pull out the stopper and just see if steam comes out of the sole plate.
Obviously this is not the only reason why an iron will not emit steam but it certainly worked for me.
Richard, January 2010
