What is the difference between compression, push-fit and soldered joints?

Nearly every small plumbing job comes down to choosing one of these three. The right choice usually depends less on the joint's merits than on whether you can get the pipe dry and whether the joint will ever need to come apart again.

Step by step

1. Understand a compression joint.A brass body, a nut and a soft brass ring called an olive. Tightening the nut crushes the olive onto the pipe and against a tapered seat. The olive does all the sealing.
2. Understand a push-fit joint.A body containing a stainless grab ring and a rubber O-ring. The pipe is pushed in past both; the O-ring seals and the grab ring stops it coming back out. A release collar lets it be taken apart.
3. Understand a soldered joint.A close-fitting copper fitting, flux, and solder melted with a blowtorch. Capillary action draws molten solder into the gap. Neat, small and permanent.
4. Ask whether the pipe can be got dry.Soldering needs a completely dry pipe; even a trickle stops the joint reaching temperature. Compression and push-fit both work on a wet pipe, which in a domestic repair is often decisive.
5. Ask whether it will need undoing.Compression and push-fit both come apart. Soldered joints have to be cut out. For anything you may want to service, use a demountable joint.
6. Ask where it will live.Compression joints should not be buried in a wall or a floor, because they can loosen. Push-fit is generally accepted in accessible positions; check the manufacturer's guidance for concealed work.
7. Match the fitting to the pipe.Plastic pipe needs a pipe insert in both push-fit and compression fittings, or the pipe collapses under the olive or the grab ring.
8. Prepare the pipe end properly.Cut square with a pipe slice, deburr, and clean. A scratched or oval pipe end will leak in any of the three systems.
9. Choose for the job in hand.Under a sink where the pipe drips, push-fit. On a valve or an appliance connection you may want to undo, compression. In a wall chase in a house being renovated, soldered by someone who does it regularly.
10. Respect the fire risk if you do solder.A blowtorch next to floorboards, joists and insulation causes real fires, often hours later. Use a heat mat, keep water to hand, and check the area repeatedly afterwards.

Tips

• For most household repairs, push-fit is the safest choice — no flame, no tools, and it works on a wet pipe.
• Always use a pipe insert in plastic pipe, in any fitting type. It is the most commonly skipped step and it causes leaks.
• Cut with a pipe slice rather than a hacksaw. A square, burr-free end is what every joint depends on.

Common mistakes

• Soldering a joint on a pipe that still has water in it — The water absorbs the heat, the joint never reaches temperature, and the solder sits on the surface instead of drawing in. It looks fine and leaks under pressure.
• Burying a compression joint in a wall or under a screed — Compression joints can relax over time and need to be accessible for tightening. A weeping joint under a floor can go unnoticed until serious damage is done.

Alternatives

• Press-fit: A fitting crimped onto the pipe with a powered press tool. Fast, permanent and flame-free, but the tool is expensive and it is really a trade choice.
• Flexible connectors: Braided hoses with threaded ends for taps and appliances. Not a pipe joint as such, but often the practical answer for connecting a fitting in an awkward space.
• Compression with a lever valve built in: Combining a joint and an isolating valve in one fitting. Worth doing whenever you are cutting into a pipe near a tap or appliance anyway.

Questions people ask