Poorly soldered copper plumbing pipe joints usually lead to pinhole leaks around the joint; however, on high pressure systems, failure could be sudden and catastrophic if not sorted out in time. Detecting a damp spot on a wall, or a musty smellin the bathrom of kitchen, is usually an indication of a leak – and if you have a basement, periodic inspection is essential. Once you identify and expose a leaky fitting, re-soldering the joints is a straightforward task.
Turn off the mains shut-off valve; this is located somewhere between the water meter and the house. Relieve water pressure by opening the tap farthest from the leaky joint.
Place a piece of sheet metal between the leaky fitting and any nearby combustible material, such as floorboards, insulation or exposed timber.
Don a pair of safety glasses and thick work gloves. Open the valve on a plumber’s propane torch and light it with a spark igniter.
Grip the fitting with a pair of channel pliers. Play the flame on the fitting while wiggling it back and forth until the solder melts and allows you to withdraw the fitting. Discard the old fitting and turn the torch off.
Cool the pipe with a cloth. Loop a strip of coarse emery tape around the end of the pipe. Apply pressure and work the tape back and forth until you abrade the joint down to bare shiny copper; calcium and mineral deposits from the slow leak will have contaminated the solder by now. Repeat with the other side of the pipe previously connected to the fitting.
Roll up a strip of emery tape. Insert it into the new fitting and twist it back and forth until the inside copper surface is shiny. Repeat with the other side of the fitting.
Apply a liberal amount of paste type solder flux to all mating surfaces of the joint and assemble the fitting. Pull about 100 mm of lead-free plumber’s solder from the reel and hold it in your left hand.
Relight the torch and play it over one side of the pipe and fitting. Keep applying heat until both the fitting and protruding pipe turn blue/black, and flux starts liquefying and bubbling out of the joint.
Withdraw the flame slightly and feed solder into the joint. Heat and capillary attraction will draw solder between both mating surfaces. Repeat with the other side of the fitting. Inspect both joints to ensure they are smooth and blemish-free.
Turn the mains shut-off valve back, on with the farthest tap still open to expel any air trapped in the system. Close the tap after air stops bubbling out and inspect the fitting for leaks.
Don’t try to melt solder into the joint. Direct the flame onto the copper until the metal is hot enough to melt solder and draw it through the joint. Do not use 50/50 solder on household plumbing – it contains lead which will contaminate drinking water.