Iron versus hard water

I like my iron a lot - it's a GE that I picked up at Walmart a couple years ago. The black looks nice, it's got some heft to it, there are a lot of steam vents (yeh, send in the quilt police) and the 6 foot cord is quite helpful at times. It does have auto shutoff but it heats up so quickly that I don't care and it's nice to know that if I get sidetracked elsewhere that it WILL shut off on it's own.

Unfortunately, the water here is very hard. The directions that came with the iron said to alternate distilled and tap water. I did for the longest time but there were some calcium deposits that would come out the steam vents when I shook the iron or pressed the extra steam button. I could deal but decided to just use distilled for a while to see if it helped.

Last night I ran out of distilled, needed my steam and filled it with tap water. It had just turned off so I pressed the power button to reheat it and all the sudden I heard steam while I watched water and brown gunk/calcium dribbling out the bottom steam vents. It made a mess of my iron board cover but it also made a mess of the sole plate. Any ideas how to clean the calcium out? Vinegar works on other items but what about in an iron? Anyone else have problems with hard water? I would love to hear what you do...