A leaking compression fitting on a copper pipe is one of the more common plumbing headaches in NZ homes, and in many cases you can fix it yourself without specialist tools. The key is understanding why it's leaking before you start tightening things — because over-tightening is just as problematic as under-tightening.
How a Compression Fitting Works
A compression fitting joins copper pipe (or sometimes plastic pipe) without soldering. It consists of three parts: the fitting body, a compression ring (also called an olive), and a compression nut. When you tighten the nut, it squeezes the olive against the pipe and the fitting body, creating a watertight seal. Most fittings used in NZ homes are either imperial or metric — check your pipe diameter before buying replacement parts.
Common Reasons a Compression Fitting Leaks
- Under-tightening — the nut hasn't been tightened enough to compress the olive fully
- Over-tightening — the olive has been crushed or cracked, or the fitting body is damaged
- Damaged or scored pipe — a scratch or burr on the copper prevents a proper seal
- Worn or displaced olive — the olive has shifted or deformed over time
- Vibration or movement — pipes that move can gradually loosen fittings
- Wrong pipe size — using a fitting rated for a different diameter
Tools and Materials You'll Need
- Two adjustable spanners or open-ended spanners (one to hold the fitting body, one to turn the nut)
- PTFE tape (sometimes called Teflon tape) — available at Bunnings or Mitre 10
- Replacement olives and compression nuts (if needed)
- Pipe cutter or hacksaw
- Fine emery cloth or wet-and-dry sandpaper
- Bucket and towels
Step-by-Step: Fixing the Leak
1. Turn Off the Water Supply
Always isolate the water supply before working on any fitting. Turn off the toby (water meter stopcock) at the boundary, or use an isolating valve if one is fitted nearby. Open a tap downstream to release pressure and drain the line. Place a bucket and towels under the fitting.
2. Dry the Area and Identify the Leak Point
Dry the fitting thoroughly with a cloth, then watch carefully to see exactly where the water is coming from — around the nut, or from the fitting body itself. This tells you whether the issue is the nut/olive or the fitting body.
3. Try Tightening First (Carefully)
If the fitting has never been fully tightened, you may be able to stop the leak by tightening the compression nut a quarter to half a turn with two spanners — one holding the fitting body still, one turning the nut clockwise. Do not over-tighten. Brass fittings can crack, and a crushed olive will never seal properly. Turn the water back on briefly to check. If it still leaks, move to the next step.
4. Disassemble and Inspect
If tightening doesn't work, turn the water off again and undo the compression nut fully. Slide the nut and olive back along the pipe. Inspect:
- The olive — look for cracks, flat spots, or heavy scoring
- The pipe end — check for scratches, burrs, or ovality; use fine emery cloth to smooth any rough spots
- The fitting body — look for cracks or damaged threads
If the olive is damaged, it must be replaced. Olives are inexpensive and available at most plumbing suppliers and hardware stores.
5. Reassemble with a New Olive
To remove a stuck olive, carefully cut it off with a hacksaw (protect the pipe). Cut a fresh, square end on the pipe with a pipe cutter, deburr it, and clean it with emery cloth. Slide on the new nut (thread facing the fitting), then the new olive. Push the pipe fully into the fitting body and hand-tighten the nut. Then tighten with spanners — finger tight plus one full turn is the standard rule of thumb for most compression fittings, but always check the manufacturer's instructions.
6. Restore Water and Check
Turn the water back on slowly and watch the fitting for a full minute. If it's still weeping slightly, try a further quarter-turn. If it continues to leak after that, the fitting body or pipe may be damaged and the fitting should be replaced entirely.
A Note on PTFE Tape
PTFE tape is not normally used on the olive or compression nut threads of a standard compression fitting — the seal is mechanical, not thread-based. Some plumbers apply a small amount of jointing compound to the olive as a belt-and-braces measure, but this is not always necessary. Follow the fitting manufacturer's guidance.
NZ Plumbing Regulations — What You Can Do Yourself
Under New Zealand law, sanitary plumbing and drainlaying is restricted work that must be carried out by (or under the supervision of) a licensed tradesperson registered with the Plumbers, Gasfitters and Drainlayers Board (PGDB). However, maintenance and repair of existing fittings — such as tightening or replacing a leaking compression fitting on a cold or hot water supply line — may in some circumstances be work a homeowner can do on their own property, but the scope of what is permitted is not straightforward. Check with the PGDB before proceeding to confirm whether your specific repair is restricted work.
If you are unsure whether your specific job is restricted work, check with the PGDB or MBIE Building Performance before proceeding.
Safety note: Never work on gas lines yourself — gas fitting is always restricted work requiring a licensed gasfitter.
When to Call a Professional
Call a licensed plumber if:
- The fitting continues to leak after reassembly with a new olive
- The copper pipe itself is corroded, pinholed, or cracked
- The fitting is on a hot water cylinder, heating system, or gas line
- You're not confident working with the water supply isolated
- The leak is inside a wall cavity or in a difficult-to-access location
- You suspect the issue is systemic (multiple fittings leaking, water hammer, or high pressure)
A qualified local plumber can be found quickly on tradedirectory.co.nz.
Master Plumbers
