solder don't stick, new tip.

[sam_sam_sam]

One note if you use a metal type of cleaning medium this is hard on a tip and you do every so often have to do this but it does wear your tip one other thing that wears out your tip is if you make it a habit of trying to clean soldering joints hole with the tip this cause the tip to be out of rounds and making hard to solder with

[kity92]

I had the same situation with my old soldering gun. You have a corrosion tip and there is no way to fix it. Don't use any sandpaper I did it but just making it worse. There is two option. Change tip and buy some cheap tips (if you soldering one time in a month) or purchase a new soldering gun because high temp and bad soldering wire are killers of tips.

-Dont use sanding paper
-Dont use tinner for clean tip
-Use clean water and sponge
-Dont use your tip like aggressive
-Stay all the time some soldering wire on tip

[mosfetratus]

steel wool or thick cotton cloth to wipe that oxide crust