Any waxy substances however, can often be cleaned off by heating the iron up to its highest setting and running it across newspaper. Oily substances can be removed with ammonia on a rag and then just rinsing. Vinegar is often recommended for a lot of irons. You just pour it on a cloth and then rub the cloth over the iron. You can also add baking soda to the vinegar for even harder cleaning.
Any build up in the vents can be a big problem as you cannot use anything harsh - scratching the base of the iron just causes massive problems in the future. You need to use something soft like a cotton bud. A great way to clean the water tank out is to pour a solution of half vinegar and half water into the tank and heat the iron up and allow it to steam well for 5/6 minutes. You then need to drain the iron and then about an hour later repeat all this with just clean water. If you don't you will have some wonderfully smelly clothes next time you iron.
I've got an iron with a very shiny bottom plate and I try never to iron over anything that could stick to the iron. However if it ever does accidentally, I wait until it cools down and use window cleaner spray with a soft cloth and it seems to work really well.
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