Hot water heater replacement. The old copper pipe seems thicker and darker than the new, and wont solder for anything. The new pipe and connectors melt the solder and flux, coating the entire joint in seconds. The old pipe will not cover "tin" or solder. No matter how long I heat it with the butane torch, the solder melts but will not stay on the pipe. Just beads and rolls off. Any help? I did clean with wire brush and then coat the pipe with flux.