I used vinegar in irons before BUT I haven't done it in my newest one yet (it's only 3 yrs old).
This is what I did. At your own risk--
I poured white vinegar into a cold iron....filled it up all the way. Let it set overnight. Plugged it in and pushed the steam button till it stopped steaming. Poured the rest of it out and filled with distilled water a few times till the vinegar smell was gone.
Still worked great till I dropped it and broke it 2 mos later.