Paella pans are most often made of thin carbon steel to quickly transfer the heat to the ingredients. The most frequent problems with these pans, is rusting from improper storage. This is easily preventable. Treat your pan properly, and it will last for many years of making paella.
Prior to the first use, fill the pan with water and a tablespoonful of cider vinegar. Boil for 10 minutes over high heat to help clean off the manufacturer’s anti-rust coating. Discard the water. Hand wash the pan with soap and water and make sure to dry thoroughly. Do this each time after using the pan. Do not wash it in the dishwasher. Never allow the pan to air dry after washing and don’t leave the pan unsealed as it will rust. You may also find that your pan takes on a "seasoned" appearance – do not worry as this is perfectly normal.
Wipe the entire pan with a vegetable or olive oil covered paper towel before storage to prevent rust. Rub a dry paper towel over the pan before use to remove the excess vegetable or olive oil. Brush rust spots off the pan with a piece of steel wool, if any occur from not completely coating the surface of the pan with oil.
When cooking with carbon steel, don’t leave an empty pan over direct heat for more than a few seconds. The metal is thin and could overheat, which will cause a dark splotch in that part of the pan. Since the stainless paella pans are made from a relatively thin one-ply material, they heat up and cool down more quickly than other pans. This is a good thing for making paella, but be aware that you shouldn’t set an empty stainless pan over direct heat. If an empty (or nearly empty) pan is left over strong heat for too long, the pan could discolour or warp. But as long as there is broth or food in the pan to absorb the heat, it will be fine. Just remember, this is not a pan that calls for pre-heating to get a good sear.