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Flux misuse causes pipe corrosion

As a plumber that takes pride in doing the job properly, you do come across work done by other plumbers that you thoroughly disapprove of. You see the same ‘schoolboy’ errors cropping up time and time again, these are simple errors plumbers make that cause customers all kinds of problems down the line.

boiler installation pipe soldering
I’m proud of my solder work, it’s part of a first rate boiler installation
In this article we’re going to expose one of the most common and destructive mistakes many plumbers are making day in, day out.

Pipe soldering is an essential part of a proper boiler installation job. These days we see more and more plastic fit joints but few homes operate without any good old soldered copper piping. I still recommend soldered copper pipes over plastic joints, it may take less skill and training to install a plastic joint but I’ve found they are more unreliable in real life and to me that’s everything.

Pipe corrosion problems

One of the more common reasons for pipe joint failure and the resultant leakage is corrosion in the pipe and in the joint. A corroded pipe rarely starts leaking when the corrosion wears right through the middle of a pipe. Usually corrosion weakens joints and causes problems for the boiler that can lead to leakage at a joint or valve. When I come out to pipes in this state & replace them, I can do some detective work to find the cause.

When I inspect failed pipe joints there are a variety of common causes. When it comes to corrosion there’s a a pattern I see time and time again, and it’s a sign of plumbers misusing a substance called ‘Flux’ when they solder a joint.

What you see is plenty of green oxidised copper and patches of broken surface on the inside of the pipe and in particular around joints. Copper is used in piping because water will take a very long time to erode the surface, where you see this kind of corrosion, it’s because something has got into the pipe.

plumbing flux

What is Flux?

In plumbing, flux is a compound used as part of soldering a pipe joint. It’s an acidic paste that is applied to the part of the copper pipe where the solder must make a bond. It cleans the joint, if you rub it on some copper and leave it a short while, it will be left gleaming when you wipe it off.

Crucially when heated, the acidic flux draws molten solder deep into the cracks of the joint and forms a clean bond with the metal. Flux is an essential part of allowing the solder to flow evenly and fully around a well soldered joint.

When Flux goes wrong!

copper pipe corrosionThe problem in plumbing is that many plumbers apply way too much flux, too carelessly and right inside the pipe joint. This means that a great excess of this acidic paste is pushed inside the pipe joint and even a layperson should see the problem with that.

Many plumbers seem unaware that this can cause a problem some time down the line, it’s one of my ‘pet peeves’ and I’d be delighted if it would stop. The flux will corrode the pipe at the joint and some will be pushed around the system to find other things to corrode, maybe inside your boiler. The bottom line is that misuse of flux is commonplace and causes problems large and small.

How to avoid bad plumbing

There’s no simple answer to getting the right plumber for your job. If you knew everything to ask, you would know enough to do the job yourself.

My advice is to try to ask questions anyway, if getting a new boiler, ask them about how they commission a new boiler, how they plan the work and if soldering is involved, you could ask about their use of flux. Don’t forget to make sure they are a gas safe plumber.

It also helps to look at online reviews and read up a little on your plumbing area of interest. You’re already doing something right by being here reading this. If you can select a quality plumber that knows their stuff, it’s well worth the effort and any extra cost over the cheapest option you can find.

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