How to Replace a Leaky Angle Stop (Shutoff Valve) Under Your Sink

Before starting any work, you must shut off the water to the entire house. Locate your main water shutoff valve, which is typically found in a basement, crawl space, or utility closet near where the water service enters your home. Turn the valve handle clockwise until it is fully closed. To drain the water remaining in the system, open a faucet on the lowest level of your home (like a basement sink) and another on the highest level. This will relieve pressure and minimize water spillage when you remove the old valve.

Prepare your workspace under the sink. Clear out any cleaning supplies or other items to create ample room to maneuver. Place a bucket directly beneath the angle stop you are replacing to catch residual water. Have several old towels ready to absorb any spills. Using an adjustable wrench, grip the nut connecting the flexible faucet supply line to the top of the angle stop. Turn the nut counter-clockwise to loosen it. Once it's loose, you can typically unscrew it the rest of the way by hand and pull the supply line away from the valve.

This step requires two wrenches to avoid damaging the pipe. Use a pair of channel-lock pliers or one adjustable wrench to grip the body of the angle stop firmly to hold it steady. Use a second adjustable wrench to grip the large compression nut that secures the valve to the copper pipe coming out of the wall. Turn the second wrench counter-clockwise to loosen the nut. This may require considerable force. Once the initial seal is broken, you should be able to unscrew the nut by hand and slide the entire old angle stop off the pipe.

With the old valve removed, slide the old compression nut off the pipe. You will see a small brass ring, the ferrule (or compression sleeve), on the pipe. It is best practice to remove this and use the new one that comes with your new valve. A dedicated compression sleeve puller is the ideal tool for this, as it removes the sleeve without damaging the pipe. If you don't have one, you can try carefully cutting a slot in it with a small hacksaw (being careful not to cut the pipe) or prying it off. Once the old hardware is removed, take a piece of emery cloth and thoroughly clean the end of the copper pipe until it is bright and smooth. This creates a clean surface for the new seal.

Take your new quarter-turn angle stop and disassemble it. Slide the new compression nut onto the cleaned pipe first, making sure the threads are facing out (towards you). Next, slide the new brass ferrule onto the pipe. The tapered end of the ferrule should face towards the valve. Now, push the body of the new angle stop onto the pipe until it fits snugly against the ferrule. Slide the compression nut up to the valve and thread it on by hand until it is finger-tight.

Just as with removal, use two wrenches for tightening. Hold the body of the new angle stop steady with channel-lock pliers or an adjustable wrench. Use a second adjustable wrench to tighten the compression nut. The general rule is to tighten one full (360-degree) turn past finger-tight. This compresses the ferrule onto the pipe, creating the seal. Do not over-tighten. Once the valve is secure, re-attach the faucet supply line to the outlet on the new angle stop. Hand-tighten the nut, then use an adjustable wrench to give it a final quarter-turn.

First, make sure the new angle stop is in the closed position (for a quarter-turn valve, the handle will be perpendicular to the pipe). Go back to the main water shutoff and turn it on *slowly* by rotating the handle counter-clockwise. This prevents a water hammer shock to your pipes. Return to the sink and use a flashlight and a dry paper towel to meticulously inspect the new valve. Wipe down the compression nut and supply line connection; the paper towel will make even a tiny bead of water obvious. If everything is dry, turn the handle on the new angle stop to the open position (parallel to the pipe). Turn on the faucet to bleed air from the line. Check one last time for any leaks around the valve stem and connections.