Step 1
Locate the water main shut-off valve and turn off the water.
Step 2
Sand the solder joint and the adjoining surfaces of the pipe joint and the pipe with sandpaper until the copper looks shiny and not dull. Wipe the sanding dust off of the pipe and joint with a clean rag.
Step 3
Apply solder flux to the old solder joint and the adjoining pipe joint and copper pipe. Do not forgo the solder flux. The flux cleans the pipe and prepares it for the solder.
Step 4
Turn on a blowtorch until you have a blue flame that extends approximately 2 to 3 inches from the torch's tip.
Step 5
Heat the existing solder until it turns a bright silver color. This means the solder has melted. Apply additional solder to the joint while you continue to heat the joint. Turn off the blowtorch once you have a consistent amount of solder around the entire joint.
Step 6
Turn on the water main shut-off and check the joint for leaks. If you locate a leak, turn off the water main and re-sweat the joint.