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Published by Mo's Plumbing and Heating
How to Fix a Leaking Pipe Joint
A joint leaking is a different problem from a pipe leaking, and it wants a different response. The instinct is to tighten it. That works occasionally and makes it permanently worse more often, because most leaking joints are not loose, they are badly made.
The Short Answer
Identify the joint type first. A compression joint gets one careful nip, no more than a quarter turn, and if that does not stop it the joint comes apart and the olive is replaced. A push-fit joint is never tightened: it is released, the pipe end is inspected and cut back if damaged, and it is remade. A soldered joint cannot be tightened at all and has to be remade from scratch. Tightening the wrong joint, or over-tightening the right one, turns a weep into a job.
Which Joint Have You Got?
Three types cover almost everything in a domestic property, and they look quite different once you know what you are looking at.
Compression: a brass body with a hexagonal nut at each end. Inside each nut is a soft brass ring called an olive, which is crushed onto the pipe as the nut tightens and forms the seal. The nut is the visible tell.
Push-fit: a plastic or brass collar the pipe simply pushes into, with a grab ring gripping the pipe and an O-ring sealing it. No nuts to turn. Released with a special collet clip or by pushing the collar in while pulling the pipe out.
Soldered: a smooth copper fitting with a neat bright ring of solder visible at the mouth. Nothing to turn and nothing to release. If it leaks, the joint is remade rather than adjusted.
Knowing which you have decides everything, because the correct response to a leak differs completely between them and applying the compression response to a push-fit joint achieves nothing at all.
Compression Joints: One Nip, Then Stop
The one case where tightening is legitimate, and it is worth doing carefully rather than enthusiastically.
With a spanner on the fitting body to stop it rotating, and another on the nut, tighten by no more than a quarter turn. Then stop and look. If the weep stops, you are finished. If it does not, do not keep going, because you are now deforming the olive rather than seating it, and a distorted olive will never seal however hard it is pulled up.
Over-tightening is the single commonest way a small weep becomes a real leak. It can crush the olive out of shape, split it, or in a bad case squash the copper pipe itself so that no olive will ever seal on that spot. At that point the pipe has to be cut back and the joint remade further along, which is a much bigger job in a confined space.
If the quarter turn does not do it, turn the water off, take the joint apart, and look. Usually you will find the olive is scored, oval, or has been over-tightened before by somebody else.
Remaking a Compression Joint
Straightforward, and the only fiddly part is removing the old olive.
- Water off, and drain the run down as far as you can.
- Undo the nut and pull the joint apart. The olive stays on the pipe, crushed in place, and it will not slide off.
- Remove the old olive. A junior hacksaw cut along it, stopping just short of the copper, lets it be split off with a screwdriver. Do not saw into the pipe. Alternatively cut the pipe back beyond the olive and use a slightly longer new section, which is often quicker if there is room.
- Clean the pipe where the new olive will sit until it is bright, smooth and free of scratches. A longitudinal scratch under an olive is a leak path and it will weep no matter how well the nut is tightened.
- Slide the nut on first, then the new olive, then push the pipe fully home into the fitting. A pipe not fully seated is the second commonest cause of a leaking compression joint.
- Tighten hand tight, then about a turn to a turn and a quarter with a spanner. It should feel like it is crushing the olive, then firming up. Stop when it firms.
- Whether to use jointing compound divides opinion. A smear of a suitable compound on the olive does no harm and helps on an imperfect pipe surface. It is not a substitute for a clean pipe and a correctly seated olive.
Push-Fit Joints: Never Tighten, Always Remake
There is nothing on a push-fit joint to tighten, and the collar is not a nut even though it looks like one on some designs. Turning it does nothing useful and can damage the grab ring.
When one weeps, there are three usual causes and all three need the joint released. The pipe was not pushed fully home, so the O-ring is not sitting on a clean sealed section. The pipe end was cut at an angle or left with a burr, which either damages the O-ring going in or leaves a path past it. Or the pipe end is scratched or scored where the O-ring sits.
To remake it, turn the water off, release the collet, and pull the pipe out. Look at the last inch of pipe. If there is any scoring, cut it back with a proper cutter, deburr it, and check it is square. Then push it fully home, which usually takes more force than people expect, and give it a gentle pull to confirm the grab ring has bitten.
One thing worth stating: an insert is essential in plastic pipe and optional-looking but not optional. Without it the plastic collapses slightly under the grab ring and the joint will eventually leak. Copper does not need one.
Why the Joint Failed at All
Worth a thought before remaking it, because a joint that was fine for years and has started weeping is telling you something a joint that never sealed is not.
A newly made joint that leaks immediately is a workmanship issue: not seated, not square, dirty, or over-tightened. Remake it and it will be fine.
A joint that has been sound for years and has begun to weep is usually movement or temperature. Pipework that is inadequately clipped moves every time the heating warms and cools, and over years that works a joint loose or fatigues the olive. If you find an unclipped run flexing when you push it, clipping it properly is part of the repair rather than an extra.
Water hammer is the other cause worth knowing: a bang in the pipes when a tap or an appliance valve shuts quickly puts a shock load through every joint in the run. If your plumbing knocks, that is worth addressing rather than living with, because it shortens the life of every joint it passes through.
And where several joints on one run are weeping at once, stop treating them individually. That is a pipework condition rather than a set of coincidences, and it usually means the run needs proper support or replacing rather than a sequence of repairs.
Joints You Cannot Get Two Spanners To
The difficulty with joints in this city's flats is rarely the technique and almost always the access. A compression joint needs a spanner on the body and a spanner on the nut, which means room for two hands and two tools at right angles to a pipe. A great many joints in converted tenement flats do not offer that.
The recurring situation is pipework run tight against a wall or a joist during a retrofit, because that was the only route available, leaving a joint with clearance on one side only. You can get a spanner on the nut and nothing on the body, so tightening the nut simply rotates the whole fitting and stresses the joint at the other end. That is how one weeping joint becomes two.
The other one is the boxed-in run. Kitchen and bathroom refits through these flats routinely enclose pipework behind panels and units, sometimes with no access at all, and the joint that starts weeping is behind a tiled boxing somebody built in 2011. The damp shows up in the cupboard next door or in the ceiling below, and the first real decision is what has to come off before anyone can even see it.
Both push in the same direction: where access is poor, cutting the section out and replacing it with a straight coupler positioned somewhere you can actually work is often less effort than fighting the original joint in place. It feels like more work and is usually less, and it leaves you with a joint you can reach next time.
When to Call Someone Out
Worth calling when the joint is somewhere you cannot get two spanners to, when it is behind boxing that has to come off, or when the pipe itself has been crushed or scored by previous over-tightening, since that means cutting back and remaking rather than adjusting. Also when several joints on one run are weeping, because that is a pipework problem rather than a joint problem and repairing them one at a time will not end. Mo, Kyle or Matt cover this, and on an awkward joint they will usually cut the section out and reposition it somewhere reachable rather than leave the same problem for next time.
Leak Detection in GlasgowCommon Questions
Only a compression joint, and only by about a quarter turn with a spanner holding the body still. If that does not stop it, stop. Beyond that point you are deforming the olive rather than seating it, and a distorted olive will never seal. Push-fit and soldered joints cannot be tightened at all.
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Read Next
Full guide
How to Repair a Leaky Pipe
Turn the water off first, then find out what the pipe is.
Can You Use Plastic Pipe With Compression Fittings?
You can, provided you fit a pipe insert, sometimes called a pipe stiffener, into the end of the plastic pipe before making the joint.
How to Solder Copper Plumbing
Clean the pipe end and the inside of the fitting until both are bright, flux both, assemble, and heat the fitting rather than the solder until the solder is drawn into the joint by capillary action.
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