How To Cap Off PEX Pipe: Step-By-Step Guide

Temporarily capping your kitchen or bathroom water supply lines is often necessary when carrying out renovation works. Sometimes, you may even want to cap the lines permanently if you want to get rid of a bathroom or laundry room. But can you cap off PEX plumbing if that’s what you have in your home? Find the answer and learn how to do it below.

How To Cap Off PEX Pipe 

Capping off PEX plumbing is possible and easy to do with a push-to-connect fitting. While originally designed for brass and copper pipes, these connectors now come with pipe stiffeners that allow you to use them with PEX and other plastic pipes.

Things You Will Need 

  • 1/2 PEX end cap (or the appropriate size if your pipes have a different diameter)
  • PEX pipe cutter
  • Emery cloth
  • Tape measure 
  • Marker 
  • Bucket (if necessary)
  • Rag (if necessary)

1. Prepare The Pipe 

You can skip this step if you’re capping a new, empty pipe. However, if you’re doing some renovations and want to cut and cap an existing pipe, you have to turn off the water and drain the plumbing system.

Depending on your circumstances, you can shut off the water only in the room you’re working in or in the entire house. Locate the most convenient shut off valve and turn the handle a quart of a turn to the off position. 

You can now drain the plumbing system by opening the highest and the lowest faucets in your house (in this order). 

Draining the pipe is only possible if you have turned off the main water supply. Otherwise, open the faucet in the room you’re working in and wait for the flow to stop after you’ve closed the valve. There might be residual water in the pipe, so place the bucket under the spot you have to cut.

2. Cut The Pipe

Based on your purpose, measure the length of the pipe up to where you want to cap it and mark the spot with a marker. 

Cut the PEX line with a specific pipe cutter – you should not use a brass or copper pipe cutter for PEX. 

PEX pipe cutters are generally sharp and produce clean cuts. However, you should check the section and remove all burrs with an emery cloth. Removing the burrs is particularly important because their presence can prevent a proper seal when installing the cap.

Wipe the pipe end with a clean rag when you’re done to remove all residues. 

3. Cap The Pipe 

Capping off old water pipes is easy with quick-connect (push-and-connect or SharkBite) stopper plugs. However, pay attention to buying a PEX-compatible water pipe stopper plug – quick-connect caps are designed for copper and brass pipes, and not all brands include a stiffener.

A stiffener is needed when sealing PEX pipes to prevent the pipe from losing its shape when installing the cap. Without this part, the cap is more likely to leak or burst under pressure when you turn the water back on.

Once you have the right fitting, slip the stiffener into the PEX pipe and slide the quick-connect cap onto the tube. Push the cap until it clicks in place and lock it with the plastic bracket by sliding it between the brass cap and the plastic push section that allows you to remove the cap.

The video below shows you how to do it: 

4. Check For Leaks

You can now turn on the water and let it fill the plumbing system – the system is filled when the water starts coming out from the highest faucet in your house. Let it run for a few minutes, then check the seal for leaks. 

If the cap leaks, the end section of the pipe might have burrs, or the stiffener is not inserted correctly. You’ll have to remove the cap and seal the pipe again.

How To Permanently Cap Off A PEX Water Pipe?

The method above is a perfect choice when you have to cap off the water lines temporarily. If you want to cap a PEX line permanently, you should use a brass end cap for the PEX pipe and crimp it in place. This method is similar to installing a valve on a PEX pipe. Here’s how to do it: 

  1. Drain the water pipe (if necessary) and remove the burrs with an emery cloth. Clean the dust and debris with a rag.
  2. Slide a crimp ring onto the pipe end. 
  3. Slide a brass end cap for the PEX pipe inside the pipe and push until it is completely seated. 
  4. Push the crimp ring back up, leaving about 1/8 of an inch from the end of the tube. 
  5. Seal the ring with a crimp tool and check the connection with a crimp ring gauge. Turn on the water and check for leaks. If the seal is leaking, cut the joint and install a new end cap.

How To Use A Crimp Ring Gauge?

A crimp ring gauge is a handy tool that allows you to check the quality of an end cap or valve connection on a PEX line. 

The tool has two slots marked with GO and NO GO. After you have crimped the ring in place, you should be able to slide the GO slot over the ring without feeling resistance. At the same time, the NO GO slot should not slide over any area of the ring.

In case you feel resistance or the NO GO slot slides over the ring after crimping it, you have to cut off the joint and replace it.

Can You Cap A Water Line Under Pressure?

No, you should never cap a water line under pressure. If you don’t have separate water shut off valves for your kitchen and bathroom, it is crucial to turn off the main water supply and drain the plumbing system before capping off sink plumbing (or any other pipe).  

Trying to cap a water line while it is under pressure could result in disaster, especially if you have an electric outlet nearby.

If you live in an old building and don’t know where the main water shut off valve is located, contact a local plumber. A specialist will not only know where to look for the valve, but some plumbers have devices that allow them to freeze the water in the pipe and cap it securely without turning off the water supply if your house doesn’t have a shut off valve.


How do you remove the PEX stiffener?

After uncapping the pipe, you can remove the PEX stiffener from inside the tube with needle-nose pliers. Get a good grip on the stiffener and push vigorously. The sleeve is designed to fit tightly into the PEX pipe, so you’ll need some elbow grease to take it out.

If it doesn’t budge, try loosening the end of the pipe with hot water. Because PEX is a plastic material, you can use heat to expand it and pull out the stiffener effortlessly. You can also use heat to straighten PEX pipes or get rid of the kinks.

Can you use SharkBite on PEX-A?

Yes, you can use SharkBite end caps and connectors on all types of PEX tubing, including PEX-A, PEX-B, and PEX-C. 

To End 

Whether you have to cap off PEX plumbing temporarily or permanently, the task is easy to tackle even by beginners. As a rule of thumb, the quick-connect cap is a good choice for temporary sealing, whereas a brass end fitting is a better choice for permanent capping. We hope this guide can help you complete the project without trouble.

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