How do I fix a compression joint that weeps?

A compression joint seals when a soft brass olive is crushed between the nut and a tapered seat. It is a very reliable joint, and almost every failure comes down to the pipe end, the olive, or how hard someone tightened it.

Safety

What you'll need

• Two adjustable spanners
• New olives of the correct size
• A pipe slice and a deburring tool
• Jointing compound or PTFE tape
• Cloths and a container

Step by step

1. Confirm it is the joint and not something above it.Dry everything and put dry paper underneath. Water runs along pipes, so the wet point is often not the source.
2. Try one quarter turn.Use two spanners — one holding the fitting body, one on the nut — so the force does not twist the pipe or the fitting. A quarter turn cures a large share of weeping joints.
3. Stop if it does not respond.If a quarter turn does not stop it, more force will not either. Beyond that point you are deforming the olive and risking splitting the nut.
4. Isolate and drain the pipe.Close the nearest isolating valve or the stopcock, open the outlet, and let the section drain. Container and cloths underneath.
5. Take the joint apart.Undo the nut and slide the fitting off. The old olive will usually be stuck to the pipe.
6. Inspect the pipe end.It must be round, square-cut, clean and free of scratches along the olive's seat area. A pipe cut with a hacksaw or scored by a grip is a common cause.
7. Remove the old olive.Cut carefully along it with a junior hacksaw without scoring the pipe, then split it off. Or cut the pipe back and use a new section with a coupler.
8. Fit a new olive.Slide the nut on, then the new olive, then push the pipe fully home into the fitting so it seats against the internal stop.
9. Use a little jointing compound.A smear of non-setting jointing compound on the olive helps it seat and seal. PTFE tape wrapped round the olive is a common alternative.
10. Tighten to hand-tight plus about one and a quarter turns.That is the usual guidance for 15mm copper. Support the fitting with the second spanner throughout.
11. Restore the water slowly and check.Open the valve gradually, then check by hand and with dry paper after ten minutes and again after an hour.

Tips

• Two spanners, always. Tightening a compression nut with one spanner twists the pipework and starts leaks elsewhere.
• Keep a few olives in 15mm and 22mm in the toolbox. They cost pennies and are the part you always need.
• A pipe end cut with a hacksaw is rarely square enough. Use a pipe slice.

Common mistakes

• Tightening progressively harder until it stops — Past about one and a quarter turns the olive is fully crushed. Further tightening extrudes it, distorts the seat and can split the nut, and the joint then leaks permanently.
• Reusing the old olive on a remade joint — It has already been crushed to the shape of the old fitting and the old position on the pipe. It will not conform to a new seat and will weep.

If it doesn't work

Questions people ask