How to Repair a Leaking Copper Pipe

Cut out the old pipe and solder in a new coupling

When a copper water pipe corrodes and leaks, or bursts from freezing, you have to fix it fast. If the leak is pinhole-sized and less than 1/2 in. of pipe must be removed, you can make the repair by cutting the pipe and soldering (“sweating”) on an ordinary pipe coupling.

But to repair longer sections, use a “sweat” coupling, which you can find at home centers and well-stocked hardware stores. You can buy a sweat coupling sized to repair 1/2-in. or 3/4-in. copper pipe. Mark the leak, shut off the main water valve and drain (or thaw and drain) the affected pipe. Cut out the damaged section (Photo 1), then measure the gap and, from the sweat coupling, cut a repair piece that’s 1 in. longer than the damaged section.

The key to a good solder joint is to keep the inside of the pipes dry, so keep a cotton rag stuffed in each pipe end to absorb dribbles of water until just before you solder. Open a faucet above that level to keep pressure from building up and dribbling more water into your repair. Then complete the steps shown in Photos 2 - 4 for a leak-proof repair. Once finished, turn the main supply valve on and check for leaks.