To solder any kind of copper pipe, regardless of size, it must be CLEAN AND CONTAIN NO WATER.
Before you begin, watch this brief instructional video on how to solder copper pipe:
Purging pipework of water can be very difficult. The first thing to do is to find a drain point below the pipe that you want to solder. Sometimes on long horizontal runs, water can sit in the pipe. You can either lift the pipe slightly towards the drain point or, if you can’t move it, attach a hose to the end of the pipe you are soldering and blow the water out.
You will need:
Lead Free solder (for potable water pipe)
(To clean the Pipe use wire wool or a kitchen pad and a good acid Flux)
TIP: Use gloves because if the flux gets in any minor cut it can sting.Scrub clean the outside of the pipe and apply your flux with a brush. Some plumbers like to apply some flux on the inside of the fitting but this can cause flux deposit inside the pipe and eventually leaks can occur.
Insert the cleaned and fluxed pipe into the fitting and position your heat mat to protect any surfaces nearby. Light your blow torch and adjust the flame so that it is stable and not too fierce. Gently heat the fitting. After a few seconds and depending on your flame heat, touch the end of you solder wire on the fitting. If it is hot enough the solder should melt and run around the fitting. Generally an inch of melted solder wire should be enough to create a water tight seal on 15mm pipe. Extinguish your torch and put in a safe place as the nozzle will be hot. Inspect the joint with your mirror. You should be able to see a thin solder all round the fitting. If you are happy use your wet rag to clean the joint of flux – old flux on a pipe turns green. Wait until your fitting has cooled and test for water tightness