I had a problem sweating some copper pipes the other day. Adding a 4′ slant fin baseboard heat. When I applied the solder it melted, but not evenly around the seam, thhere were gaps in between. This made me apply me solder sort of like trying to fill in the gaps. Afterwards, I deceided to thin the pipes, join the pieces together and then sweat it. While trying to tin the pipes the solder would like flow it just rolled off. Also the flux turned dark during the heating process.
Can someone tell me what I was doing wrong.
btw, it took many tries, but I finally got it together.