Symptoms
- Slow drip specifically at a compression nut joint
- Leak worse under water pressure
- Fitting may look slightly crooked or unevenly tightened
- No leak elsewhere along the same pipe run
Likely causes
- CommonCompression nut not tightened enoughThese fittings rely on the nut compressing a ferrule tightly around the pipe, and under-tightening is a very common cause of drips.
- CommonFerrule not seated straight or pipe not cut squarelyAn angled or rough pipe end prevents the ferrule from forming a complete seal around the pipe.
- PossibleReused ferrule from a previous connectionFerrules deform to fit a specific pipe once compressed and generally shouldn't be reused on a new connection.
- Less commonDamaged or scratched pipe surface at the ferrule locationA scratch or dent on the pipe can prevent the ferrule from sealing even when properly tightened.
What to do
- Shut off water to the affected line before attempting to adjust the fitting.
- Try tightening the compression nut a quarter turn at a time with two wrenches (one to hold the fitting body steady, one to turn the nut).
- Turn water back on briefly to test after each small adjustment, since overtightening can crack the fitting or the pipe.
- If it still leaks, shut off water again and disassemble the fitting fully.
- Cut the pipe end square with a proper pipe or tubing cutter if it looks angled or damaged.
- Install a new ferrule (never reuse an old one) and reassemble, hand-tightening first, then snugging with a wrench about a half to three-quarters turn past hand-tight.
- Test again with water on, checking closely for any remaining seepage.
Tools and parts
- Two adjustable wrenches
- Tubing cutter
Compression fitting ferrule and nutSearch: “compression fitting ferrule replacement”
When to call a pro
Call a plumber if the leak continues after replacing the ferrule and reseating the fitting properly.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.