Copper pipe pinhole leak — causes and repair
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Most likely cause & what to check
Pinhole corrosion in copper pipes is caused by aggressive water chemistry (low pH, high oxygen content, or the presence of certain dissolved minerals) attacking the pipe wall from inside. It is more common in soft water areas and in newer copper pipe systems. The result is a small hole that causes a fine spray or steady drip.
Turn off the water supply immediately. If the leak is on the cold mains, turn off the main stopcock. If it is on the heating system, close the filling loop and use the boiler isolation valves.
For an emergency temporary repair: proprietary pipe repair clamps (£8–£15 at any DIY store or plumbers merchant) bolt around the pipe and compress a rubber gasket over the hole. These are a temporary solution only — they should not be left long term.
For a permanent repair: drain the section, cut out 50mm either side of the affected section with a pipe slice (a wheel cutter that does not require straight strokes like a hacksaw), and fit a slip coupling (a push-fit coupler with no central stop, designed for making repairs in place). This requires no soldering.
If multiple pinholes are found, this indicates systemic corrosion in the pipework and you should have a plumber assess the full run. In hard water areas, the inside of old pipes can be heavily scaled; in soft water areas, the copper itself corrodes. The long-term fix may be re-piping the affected section.
Check for any contributing factors: excessive flow velocity in undersized pipework, chemical contamination in the heating system (treat with inhibitor), or flux residues from poor soldering during installation (flux left inside a joint can cause localised erosion-corrosion).
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Frequently asked questions
What causes pinhole leaks in copper pipes?
The most common causes are aggressive water chemistry (slightly acidic water that corrodes copper from the inside), electrolytic corrosion where copper contacts dissimilar metals, or mechanical erosion where high-velocity water wears through bends over years. Pitting corrosion is more common in Scotland and parts of Wales where water is naturally soft.
Can I repair a pinhole leak in copper pipe myself?
A temporary repair with a push-fit pipe repair clamp or lead-free solder patch is within DIY capability, but a permanent fix requires cutting out the affected section and replacing it with new copper or plastic pipe and proper fittings. This requires turning off the water supply and basic plumbing skills.
Should I replace copper pipes throughout if I find one pinhole leak?
Not necessarily — one pinhole does not mean all pipes are failing. However, if your property is older and you find multiple pinholes in the same pipe run, it suggests the water chemistry is attacking that section of pipework. A plumber can assess whether localised replacement or whole-system repiping is more cost-effective.