Compression fitting leaking — how to fix it
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Most likely cause & what to check
Turn off the water to the affected section — use the isolating valves either side of the fitting, or the main stopcock.
Dry the fitting completely with a cloth. Wait a few minutes and check exactly where the drip is coming from: the nut where it meets the fitting body, or the pipe entry point.
Try tightening the nut first: use two spanners — one to hold the fitting body still, one to tighten the nut. A quarter turn anticlockwise (backing off slightly) and then a half turn tighter may reseat the olive and stop the leak.
If tightening doesn't fix it: undo the nut completely. Inside you'll find an olive — a small brass or copper ring that has been compressed onto the pipe to form a seal. If the olive is deformed or has a split, replace it.
To replace an olive: slide the old one off (you may need to cut it if it's stuck fast), clean the pipe, and slide a new olive on. Reassemble the fitting — do not use PTFE tape on the olive itself, but some plumbers wrap a small amount around the olive.
If the pipe end is damaged or the fitting body is cracked: replace the whole fitting. Compression fittings are relatively straightforward to swap.
After remaking the joint, restore water pressure slowly and watch for 5 minutes. Check again after 24 hours — sometimes a slow weep only becomes visible over time.
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