

This guide provides comprehensive, step-by-step instructions for replacing a leaky angle stop (the shutoff valve under a sink) connected to a copper pipe. The process involves shutting off the main water supply, removing the old valve and its compression fittings, preparing the pipe, and installing a new quarter-turn compression-style angle stop.
Best for advanced DIYers and professionals with basic plumbing knowledge. Requires Adjustable Wrench.
The first critical action is to completely stop the flow of water to your entire house. Locate your main water shutoff valve, which is typically found in the basement, a crawl space, a utility closet, or outside near the water meter. Turn the valve handle clockwise until it is fully closed. For a lever-style valve, turn it so the handle is perpendicular to the pipe. Once closed, relieve the pressure in the pipes by opening a faucet on the lowest level of your home (like a basement sink or outdoor spigot) and the faucet connected to the valve you are replacing. Let them run until the water stops flowing.
Prepare your work area. Clear everything out from under the sink to give yourself ample room to work. Place a bucket directly under the angle stop you are replacing to catch residual water that will drain from the pipes. Lay down several old towels around the bucket to protect the cabinet from water damage.
This is the most critical step. You must use two wrenches. Place one wrench on the body of the angle stop and turn counter-clockwise. At the same time, use a second wrench to grip the copper pipe coming from the wall (the stub-out) to hold it firmly in place, preventing it from turning. Loosen the large compression nut that secures the valve to the pipe. Once loose, you can finish unscrewing it by hand and slide the old valve off the pipe.
With the valve removed, you will see the old compression nut and a brass ring called a ferrule on the copper pipe. Both must be removed. The nut should slide off. The ferrule can be stubborn. The best method is to use a dedicated ferrule puller tool, which grips behind the ferrule and pulls it off without damaging the pipe. Alternatively, you can carefully cut a slot into the ferrule with a small hacksaw or rotary tool, being extremely careful not to cut into the copper pipe itself. Once cut, you can pry it open with a flathead screwdriver and remove it.
Once the old fittings are off, thoroughly clean the end of the copper pipe stub-out. Use a piece of emery cloth or fine-grit sandpaper to polish the outside of the pipe where the new ferrule will sit. The goal is to remove any old pipe dope, corrosion, or burrs, creating a perfectly smooth surface for a watertight seal. Wipe the pipe clean with a dry rag when finished.
Take your new angle stop and disassemble the compression fitting. Slide the new compression nut onto the cleaned pipe first, ensuring the threads face towards the end of the pipe. Next, slide the new brass ferrule onto the pipe. Push the body of the new angle stop onto the pipe until it seats firmly against the ferrule. The pipe should go about 1/2 inch into the valve body. Hand-tighten the compression nut onto the valve body until it is snug.
Using the same two-wrench technique as before, tighten all connections. Use one wrench to hold the body of the new angle stop steady, preventing it from turning. Use the second wrench to tighten the compression nut onto the valve. After hand-tight, give it one-half to one full turn with the wrench. Do not overtighten, as this can damage the ferrule or the valve. Next, reconnect the faucet supply line to the outlet of the new valve. Hand-tighten the coupling nut, then give it a gentle quarter-turn with a wrench.
Double-check that the new angle stop's handle is in the closed (off) position. Go back to your main water shutoff and turn it on SLOWLY. Let the pipes fill with water gradually to prevent water hammer. Listen for any sounds of rushing water. Go back to the sink and meticulously inspect the new valve for any signs of water, no matter how small. Check around the large compression nut and the faucet supply line nut. If everything is dry, place a dry paper towel under the valve, then slowly turn the handle on the new angle stop to open it. Let the water run at the faucet for a minute to clear out any air. Perform one final check for leaks at all connections.
Once you are confident there are no leaks, dry the entire area, including the pipes, valve, and cabinet floor. Remove the bucket and wet towels. Organize your tools and return any unused supplies. It's a good practice to check on the new valve again after an hour and then a day later to ensure no slow leaks have developed.
Solution: To avoid this issue: Be mindful of this warning and take appropriate precautions.
Solution: A basin wrench is specifically designed for reaching these tight spaces. An extendable model can make this easier.
Solution: Turn the water on slowly to prevent a sudden pressure surge, known as a water hammer.
Solution: To avoid this issue: Be mindful of this warning and take appropriate precautions.
Solution: To avoid this issue: Be mindful of this warning and take appropriate precautions.
Solution: Check the unit again after one hour for leaks.
Solution: To avoid this issue: Be mindful of this warning and take appropriate precautions.
Apply penetrating oil, like Blaster PB Penetrating Oil, directly to the nut and ferrule. Allow it to soak for 15-30 minutes before attempting to loosen it again with your adjustable wrench. If it's still stuck, you may need to carefully cut the old ferrule off with a small hacksaw or specialized tool, taking care not to damage the copper pipe itself.
Ensure the copper pipe is clean, smooth, and free of burrs or scratches where the new ferrule will sit. Hand-tighten the compression nut first, then use your adjustable wrench to tighten it an additional half to three-quarters of a turn. Avoid overtightening, as this can damage the ferrule or pipe, but ensure it's snug enough to prevent drips.
Yes, absolutely. Shutting off the main water supply is crucial to prevent significant flooding when you remove the old valve. Always relieve any remaining water pressure by opening a nearby faucet after shutting off the main supply, before starting work under the sink.
For a DIY beginner, expect this project to take approximately 1 to 2 hours. This accounts for time to gather tools, carefully follow each step, and troubleshoot minor issues like a stubborn old valve or initial small leaks. Taking your time will help ensure a successful installation.
Yes, push-fit angle stops are a great alternative, especially for beginners, as they often simplify the installation process. They eliminate the need for compression nuts and ferrules, requiring only proper preparation of a clean, deburred, and unmarred copper pipe for a secure connection. Ensure the pipe is fully inserted into the fitting.
You will absolutely need a heavy-duty bucket, like the Unger 6 Gal. Heavy-Duty Plastic Bucket, positioned directly under the work area. Additionally, have an abundance of absorbent towels, such as WYPALL L40 Towels or Scott Rags, ready to quickly soak up any residual water from the pipes, even after the main supply is off.
Yes, it is highly recommended to always use the new compression nut and ferrule that come with your new angle stop. Reusing old parts significantly increases the risk of leaks because they may have been deformed, worn, or compromised during previous tightening, preventing a proper seal with the new valve.
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30 min | 10 Steps