I have heated up solder joints that I’ve recently made before to disassemble them. But the other day, when I wanted to remove an old valve, I couldn't melt the solder. Is it possible to melt old solder and remove the fittings?

I need to remove a series of valves and there is little piping to play with above the floor, so it would be best if I could melt the soldered joints and remove them instead of cutting the pipe. When I tried, I did have the system drained.

Monte Joe