Can I reuse a fitting on a PEX to brass connection?

Look at what holds the pipe on.

• A thick ring at the pipe end, sitting tight against a shoulder on the brass. That is a cold-expansion joint. Uponor's ProPEX system is the common one. The ring and pipe were stretched over the fitting and shrank back onto it.
• A copper or stainless ring squeezed around the pipe. That is a crimp or clamp joint. Some clamp rings have a small folded "ear" that was pinched shut.
• A collar the pipe disappears into, with no ring at all. That is a push-fit fitting. It grips the pipe from inside with a toothed ring.
• Hex flats and threads where the brass meets another brass part. That is the threaded end, and it is the one people usually mean when they say a fitting "unscrews."

If you can't tell, look for a brand name stamped on the brass, because the maker's instructions decide what is allowed. The code agrees. Section 605.16.2 of the 2024 International Plumbing Code says "Mechanical joints shall be installed in accordance with the manufacturer's instructions."

Yes, if the fitting is brass. Uponor's installation guide says "Brass ProPEX fittings can be disconnected and reused. EP fittings must be discarded." EP means engineered polymer, the plastic version. Uponor says the same about repairs: "Do not reuse or reclaim EP fittings."

Two things follow from that.

First, "reusable" describes the brass body. The pipe end is another matter. Uponor's guide covers a joint that did not seat properly: if the ring sits more than 1 millimeter off the fitting shoulder, the connection must be replaced. To redo it, the installer makes a fresh square cut on the pipe a set distance back from the fitting, 2 inches for the smaller pipe sizes, before making the new connection. You don't re-seat the old pipe end. You cut back to clean pipe.

Second, cutting back only works if there is slack. Uponor also sets a minimum distance between ProPEX fittings, so a tight spot behind a wall may not leave room to redo it.

Crimp and clamp rings. The maker's guidance is about not redoing a bad one. Zurn's guide says "Do not try to save time by recrimping a crimp that does not gauge properly. The fitting must be cut out and replaced." Its instructions for clamp rings say the same: if the pinch ear did not fully close, the ring is cut out and replaced. If you're taking a crimped joint apart, plan on new rings and a fresh cut in the pipe.

Push-fit fittings. These are the ones people most want to reuse, and the makers are the most cautious. SharkBite's FAQ says its fittings "can be reused for testing purposes but any fitting used repeatedly for testing should not be used in a permanent installation." Its installation guide says the brass push fittings "are intended to be a permanent connection and aren't designed for repeated connection and disconnection after the installation," though a fitting can be removed with a disconnect clip, tongs or a disconnect tool. Zurn's push-fit fitting instructions include a check before reuse: make sure the tube liner is still in the fitting, and inspect the tube end "to be sure it was not damaged, gouged or scratched as it was removed from the fitting."

If the pipe end is marked, cut it back to smooth pipe first, and confirm you have enough length to do that.

This is the most forgiving part, because threads don't wear out the way a ring does. If a brass PEX adapter screws into a brass elbow, valve or stub, unscrewing it and screwing it back in is normal work. Uponor's guide lists brass male threaded adapters for PEX. What matters is the sealant.

Zurn's guide states that "PTFE tape is the only recommended thread sealant for fittings used with Zurn PEX." It also warns that "Conventional pipe thread compounds, putty, mineral or linseed oil-based products, and unknown mixtures should never be used as these materials may cause damage to the pipe and fitting." Uponor says "Do not use petroleum or solvent-based paints, greases or sealants on Uponor PEX piping." The reason is the plastic on the other side of the adapter. Some thread compounds attack it.

So the routine is straightforward. Clean the old tape and residue off both sets of threads. Wrap new PTFE tape on the male threads. Thread the parts together and stop when the joint is snug. Don't chase a drip by cranking harder, because brass and thin-walled fittings can be damaged. If a threaded joint still weeps after a proper re-tape, replace the part rather than adding more compound.

Support matters too. SharkBite's guide says to make sure piping is "properly supported so it doesn't create a side load on the fitting, which could leak." A stub that flexes every time a valve is turned will loosen its own threads.

Test every reworked joint under pressure, and do it with the wall still open. SharkBite's FAQ says "It is also recommended to pressure test the system prior to sealing up the wall." At home, that means turning the water back on slowly, wiping the joint dry, and watching it for several minutes. A dry paper towel wrapped around the fitting shows a weep you can't see. Then run the meter test from how to do a water meter leak test with everything else off.

Replace instead of reuse when the fitting is plastic (EP), when a crimped ring can't be cut back, when a push-fit has been taken apart more than once, or when the pipe end is scored. Brass meeting steel or copper raises a separate corrosion question, covered in what a dielectric union is.

If a joint is behind a finished wall, under a sink you can't reach, or you can't shut the water off to it, call a licensed plumber. HQ Plumbing & Air offers 24/7 emergency service, and you get an upfront price and a free estimate before work starts. For choosing pipe types in the first place, see PEX vs CPVC pipe. If the fitting is a valve, a shut-off valve leaking at the handle is a different fix. And if you found water under a cabinet, start with what to do about a leak under the sink.

Here's the rule to remember. Brass bodies and threads can go again. Rings, plastic fittings and scored pipe ends get replaced.