It's possible your tip is contaminated, sand it all the way down and re tin.

I have never used flux when soldering wires, not saying it's wrong.
This one has a hi and low depending on how far you pull the trigger. Radio shack special,150/230 watts, the solder comes in different diameters and say rosin core solder on the roll.

Now I think it's different than the solder I have to solder copper pipes?

I worked for 8 years at a scale company. One of my jobs was to replace 16 pin IC chips in digital display boards. Sometimes there was like 12 chips per board X 16 pins. That's a lot of soldering with one of these and a solder sucker.