How do I get the built up gunk off my iron?

nail polish remover

It kind of depends on what caused the gunk in the first place, but one of these methods should work for you:

http://www.wikihow.com/Clean-the-Bottom-of-an-Iron

Turn on the iron and let stand for a few minutes, once it's very hot, you can use a clean towel to swipe off the gunk. Use a towel you don't mind getting ruined.

Quilt shops sell the products for this problems.even JoAnn does too

Years ago when I actually ironed, I would use easy-off oven cleaner to get rid of the burnt on gunk. Worked great. I assume they still sell the stuff.

Dritz at JoAnn and Faultless is another brand (used to get it at WalMart). If the gunk is heavy, do it in a room that you can close off since it will smoke. My Rowenta gets very hot and fast so I'm always getting some poly melted onto it.

Take a piece of foil lay on ironing board ,pour salt on top of foil, then with your iron Hot iron over and over the salt. Repeat if necessary. Don't forget to wipe salt off the iron when finished.

Borax

Used fabric dryer sheets can be used to clean an iron. Turn the iron to low temperature and just wipe.

.

Fill the water chamber with vinegar and water, set it all the way to the hottest setting, and place it on an old rag or kitchen towel and let the steam work the gunk out.

Use iron off. It's available at most fabric stores.

Thank you all for the great advise. You have saved me buying a new iron!!!