New tub valve - Solder not working

I have a new Moen tub/shower valve and the solder isn't getting drawn in and making a nice seal like it should.

I removed the old valve from the wall and it still had the 4 pieces of copper attached to it. Down in the garage I used my mapp gas torch to heat up & remove the old 1/2" copper, no issues. The new valve has a finish to it that doesn't look like solid brass, so I assume it's some kind of alloy.

I prepped the valve and copper with medium steel wool, made sure my hands were clean, fluxed everything and lined it up. It gets hot enough for the lead-free solder to just get crumbly, or melt on to the floor. After the first try, I took it apart, and there wasa practically no new solder in the joints. Sigh. Tried again, a little more heat, but no success.

Before I removed my old valve, I had to install a couple brass ball valves on the house copper. I soldered them with the same flux & solder, easy, fast, flawless. So I can't figure out why this new valve is giving me such grief. There's nothing in the instructions about any special requirements.

Oh, of course the valve has warnings about not heating it up too much because of the plastic parts inside it. Great.

Well I guess I got it now. I took out the innards and heated that sucker up a LOT. Finally the solder did it's thing. Dang, I never had something that needed so much heat. Live and learn.

Welcome to the world of 100% lead free. Back in the day brass had a small amount of lead that would help in soldiering process.

I remember doing some soldering back in the 80s when I was still a teen, and it was super easy. When I bought new solder, it was lead free and yeah, noticeably less easy to work with.

I had another issue though, my torch is done. It was just a spin on hardware store special, and wasn't letting enough gas out, and wouldn't shut off correctly. Garbage. I borrowed a Bernzomatic from a friend, and it was 10x more powerful. Did the job in no time. I'll be buying one Monday.