What you need to know before you start

PEX fittings fail when they crack, leak, or corrode — usually at the connection point where the tubing meets the fitting itself. Replacing one takes about 15 to 30 minutes per fitting if you have the right tool, and the job is straightforward enough that most homeowners can do it without experience. The catch is that you must own or rent a PEX crimping tool or expansion tool, depending on which fitting system your pipes use. Without it, you cannot make a watertight seal.

The two main PEX systems are crimp rings (the most common) and expansion fittings. Crimp systems use a metal ring that you squeeze onto the tubing with a crimper; expansion systems use a fitting that you push into the tubing after expanding it with a special tool. You cannot mix the two — if your existing fittings are crimped, you must use crimp fittings to replace them. Check your current fittings before you buy anything.

Key Takeaways

  • PEX fittings come in two types — crimp and expansion — and you must match the type already in your system or the new fitting will not seal.
  • You need a crimping tool or expansion tool to complete the job; renting one costs $20 to $40 per day at most tool rental shops.
  • Shut off the water to the section you are working on before you cut or remove any fitting.
  • The actual replacement — cutting out the old fitting, inserting the new one, and crimping or expanding — takes 15 to 30 minutes once you have the tool and materials.
  • Test the connection under pressure before you close up walls or ceilings.

Gather your materials and tools

Before you start, collect everything you need in one place. You will need a replacement fitting (the same type and size as the one you are removing), PEX tubing (if the old tubing is damaged), a crimping tool or expansion tool, a tubing cutter, a deburring tool or utility knife, and a bucket or towel to catch water.

The fitting itself costs $2 to $8 depending on the type and size. If you are using a crimp system, you also need crimp rings — these are usually sold in packs of 10 or 25 for $3 to $6. Renting a crimping tool runs $20 to $40 per day; expansion tools rent for about the same. Home Depot, Lowe's, and local tool rental shops all carry both. If you plan to do this job only once, renting is cheaper than buying. If you own an older home with PEX that fails often, buying a tool ($40 to $150) may pay for itself in a year or two.

Turn off the water and drain the line

Locate the shutoff valve for the section of pipe you are working on. If the fitting is on a hot water line, shut off the hot water heater as well. Open the nearest faucet downstream of the fitting to release pressure and let water drain out.

If you cannot find a shutoff valve for just that section, you will have to shut off the main water supply to the house. This is why many plumbers recommend installing shutoff valves at the point where water enters each room or appliance — it saves time on jobs like this one. If your house does not have them, now is a good time to add them while you have the system open.

Remove the old fitting

Use a tubing cutter to cut the PEX tubing on both sides of the bad fitting, about 1 inch away from the fitting itself. A tubing cutter is a small hand tool that looks like a pipe wrench with a circular blade; it costs $8 to $15 and makes a clean, straight cut. Do not use a hacksaw or utility knife — they crush the tubing and leave burrs that prevent a new fitting from sealing.

Once you have cut both sides, pull the old fitting out. If it is stuck, use a pair of pliers to wiggle it gently side to side. Use a deburring tool or the back of a utility knife to smooth the inside edge of each cut piece of tubing — any rough edge will prevent the new fitting from sliding in fully and will cause a leak.

Install the new fitting with a crimp system

If your system uses crimp rings, slide a crimp ring onto one end of the tubing, then push the new fitting into the tubing as far as it will go by hand. The fitting should go in about 1 inch. Once it is seated, slide the crimp ring up so it sits on top of the connection point where the tubing meets the fitting.

Place the crimping tool over the ring and squeeze the handles together firmly until the tool clicks or stops. Do not squeeze twice — one full squeeze is enough. The ring should now be compressed around the tubing and fitting, creating a watertight seal. Repeat this process on the other side of the fitting. If you are replacing a section of tubing as well, connect both ends the same way.

Install the new fitting with an expansion system

If your system uses expansion fittings, insert the expansion tool into one end of the tubing and squeeze the handles to expand the tubing slightly. Remove the tool, then push the new fitting into the expanded tubing by hand. The fitting should slide in smoothly and seat fully. The tubing will contract back around the fitting as it cools, creating the seal.

Repeat on the other side if needed. Expansion systems are often faster than crimp systems because you do not have to position a ring, but they require a more expensive tool ($60 to $150 to buy, or $30 to $40 to rent). Both systems are equally reliable when done correctly.

Test the connection and turn the water back on

Before you close up any walls or ceilings, turn the water back on slowly and watch the new fitting for leaks. Let the water run for at least 30 seconds. If you see water dripping from the connection, turn off the water when ready and redo the crimp or expansion — the seal did not hold.

If the connection is dry, let the water run for a few minutes to make sure the seal holds under normal pressure. Once you are confident the fitting is not leaking, you can proceed with any finishing work. If you had to replace a section of tubing as well, test both connections before closing anything up.

Frequently Asked Questions

Can I use a crimp ring on an expansion fitting or vice versa?

No. The two systems are not compatible. A crimp ring will not seal an expansion fitting, and an expansion fitting will not work with a crimp ring. You must match the type of fitting to the type of system already in your pipes.

What size fitting do I need?

PEX fittings come in sizes that match the tubing diameter — usually 1/2 inch, 3/4 inch, or 1 inch. Look at the tubing connected to the old fitting or check your home's plumbing documentation. If you are unsure, bring a piece of the old tubing to the hardware store and compare it to the size labels on the shelf.

How long does a PEX fitting last after replacement?

A properly installed PEX fitting should last 20 to 50 years, depending on water quality and temperature. Crimp and expansion fittings have similar lifespans. If a fitting fails within a few years, the problem is usually installation error — an incomplete crimp, a loose expansion, or a burr inside the tubing that prevented a full seal.

Do I need to use new tubing if the old tubing is still good?

No. If the tubing is not cracked or damaged, you can reuse it. Just cut out the bad fitting, smooth the cut ends with a deburring tool, and connect the new fitting to the existing tubing. You only need new tubing if the old section is kinked, cracked, or too short to work with.

What if I crimp the ring twice by accident?

A double crimp will over-compress the ring and may damage the tubing or create a weak seal. If you realize you have done this, cut out that section and start over with a new piece of tubing and a new fitting. It is faster and safer than trying to salvage the connection.