PLUMBCRATE
How to solder copper pipe (end-feed joints, UK guide)
Quick answer: to solder copper pipe, isolate and drain the water, cut the pipe square and deburr it, clean the pipe end and inside the fitting until bright, apply a thin coat of flux, push the pipe fully into an end-feed fitting, heat the fitting evenly with a blowtorch and feed lead-free solder into the joint until a complete ring appears. Let it cool undisturbed, wipe off flux residue and flush the system.
What you need
- End-feed copper fittings such as a 15mm straight coupler, 15mm elbow or 15mm tee, to suit your pipe size.
- Lead-free solder wire. Use lead-free solder on drinking water pipework.
- Flux, for example Powerflow soldering flux or LA-CO regular flux, plus a flux brush.
- A pipe cutter, deburring tool, wire wool or abrasive cloth, and a fitting brush.
- A blowtorch (butane or propane), a heat-resistant soldering mat, and a damp cloth.
Browse everything for the job in jointing, soldering and sealants.
Step by step
- Isolate and drain. Turn off the supply and drain the pipe. Solder will not take on a pipe with water in it; steam pushes the solder out.
- Cut square. Use a pipe cutter for a clean, square end, then remove the burr inside and out.
- Clean until bright. Rub the outside of the pipe end and the inside of the fitting socket with wire wool or abrasive cloth until the copper is shiny. Clean metal is the key to a sound joint.
- Flux both surfaces. Brush a thin, even coat of flux over the cleaned pipe end and inside the socket. Do not overdo it.
- Assemble. Push the pipe fully home into the fitting and give it a slight twist to spread the flux. Wipe off excess flux.
- Protect the area. Put a soldering mat behind the joint and keep heat away from plastic, cables, valves with rubber seals and timber.
- Heat the fitting, not the solder. Play the flame over the fitting so it heats evenly. When the flux starts to sizzle and the copper changes colour, touch the solder to the edge of the joint.
- Feed the solder. The heat should draw solder into the joint by capillary action. Stop when a bright ring of solder shows all the way round.
- Leave it to cool. Do not move the pipe for 20 to 30 seconds while the solder sets.
- Clean and flush. Wipe away flux residue with a damp cloth once cool, then flush the pipework to remove flux from inside before use.
Safety
- Never solder near gas pipework that is live. Gas work in the UK must be done by a Gas Safe registered engineer.
- Keep a fire extinguisher or water to hand and check the area for smouldering material for some time after you finish, especially under floors and in lofts.
- Work with ventilation, and wear eye protection and gloves. Flux can irritate skin.
Prefer not to use a flame?
Compression fittings or press-fit fittings join copper without heat. See push-fit vs compression vs solder vs press-fit to choose.
FAQs
What flux should I use for copper pipe?
Use a flux made for plumbing soldering on copper, applied thinly to clean metal. Follow the instructions on the flux and flush the system after soldering.
Why won't my solder joint take?
The usual causes are water left in the pipe, dirty copper, too little or burnt flux, or heating the solder instead of the fitting. Drain the pipe, clean back to bright copper and re-flux.
Do I need lead-free solder?
Yes for drinking water pipework. Lead-free solder is the standard choice for domestic water supplies in the UK.
How much solder does a 15mm joint need?
Roughly a length of solder similar to the pipe diameter, so around 15mm of wire for a 15mm joint. Stop when you see a complete ring.