Fixing a leaking compression joint
⚠️ Turn off and drain the relevant pipe section before starting.
Compression joints are one of the most common pipe fittings in UK homes, and when they start to weep or drip, it's often one of the first plumbing problems homeowners tackle. The good news is that a leaking compression joint rarely means you need to call a plumber — most times it's a simple fix you can manage yourself in under an hour. These fittings are incredibly reliable, but they can develop minor leaks due to vibration, age, or simply needing a gentle tighten. This guide walks you through the straightforward process of diagnosing and fixing the problem, from the quickest temporary solution to a more permanent repair. If you've got basic tools and half an hour to spare, you'll likely have your joint sealed up without any fuss; however, if the pipe itself is damaged or you're not confident working with water systems, it's worth calling a Gas Safe registered engineer.
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Most likely cause & what to check
Turn off the water supply and drain the section of pipe.
Dry the joint completely and tighten the nut a quarter-turn. Turn the water back on slowly and check — often this resolves a minor weep.
If it still leaks, turn off again. Undo the nut completely and slide it back along the pipe to expose the olive (the small brass ring).
Wrap 4–5 turns of PTFE tape around the olive before re-tightening. This often seals a weeping olive without needing to replace it.
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Frequently asked questions
Can I just tighten the nut without draining the pipe?
Technically you might get away with it for a very minor weep, but you'll make a mess and risk water damage. Always drain the section first — it takes two minutes and gives you a dry joint to work with, making the fix much more reliable and safe.
What is PTFE tape and where do I buy it?
PTFE tape (also called plumber's tape or thread seal tape) is a thin white tape that seals threaded connections. You'll find it at any DIY store, plumber's merchant, or supermarket for just a couple of pounds — it's an essential item to have in your toolkit.
How tight should I actually make the nut?
Hand-tight (as snug as you can comfortably turn it by hand) plus a quarter-turn with a spanner is the golden rule. Over-tightening damages the olive and often makes leaks worse, so resist the urge to crank it hard.
What's the difference between an olive and a ferrule?
In UK plumbing, both terms refer to that small brass ring that creates the seal inside a compression fitting — olive is the more common term here. It compresses onto the pipe when you tighten the nut, so if it's damaged or deformed, it won't seal properly.
Do I need to replace the entire fitting if it keeps leaking?
Not necessarily — if the olive is damaged, you can often just cut the pipe back slightly, fit a new olive, and reconnect using the same fitting body. Only replace the whole fitting if the internal thread is damaged or if cutting back isn't practical.
Can a leaking compression joint cause water damage if left?
A slow weep might take weeks or months to cause serious damage, but a steady drip will absolutely damage joists, floorboards, and plasterwork over time. It's worth fixing promptly rather than hoping it'll stop on its own.