How to Stop Kilner® Clip Top Jars From Leaking: Fixes That Work

Quick answer

Most Kilner® clip top jars leak because the rubber seal is worn, hardened or the wrong size, not because the jar itself has failed. Remove the seal, check it for cracks, flattening or a loose fit, and replace it with a seal matched to your jar's capacity. If a new seal still leaks, inspect the glass rim and the metal clip for chips or bending — at that point, replace the jar rather than the seal.

Start by Confirming Where the Leak Comes From

Before you replace anything, find out whether the jar leaks at the seal, at the rim, or only when tipped. Fill the jar two-thirds with water, close the clip, and stand it on a dry paper towel for ten minutes. If the towel stays dry, the seal is holding under normal standing conditions and your problem is likely tilt-related rather than a failed seal.

Next, lay the jar on its side on a dry towel for ten minutes. A leak here points to the seal-to-rim contact. Finally, turn it upside down briefly. Leaks at this stage usually mean the seal is compressed or the clip is not pulling the lid down evenly. Note exactly which test fails — that single detail decides whether you replace a seal, adjust a clip, or retire the jar.

Check the Seal Before You Blame the Jar

The rubber seal is the only soft part in the system, so it fails first. Take it out and look for three things: visible cracks or a chalky surface, a flattened cross-section where it used to be round, and whether it still sits snugly in the lid groove without falling out when you turn the lid over.

A seal that has hardened will not compress enough to fill the gap between lid and rim, which is why a jar that sealed perfectly last season can start weeping this season. Seals are sized to the jar, so a seal bought for a larger jar will not seal a smaller one properly even if it looks close. Match the seal to the jar's stated capacity rather than stretching a bigger one to fit.

Inspect the Rim, Lid and Clip

Run a fingertip around the glass rim. A chip, a nick or a moulding ridge that catches your nail will create a channel water can travel through no matter how new the seal is. Small chips near the rim are the one fault you cannot fix with a replacement part.

Check the lid for dents or a bent edge, and check that the clip's wire sits centred and pulls the lid down squarely. A clip that has been bent outwards — often from being forced over a stiff new seal — applies uneven pressure, so one side of the lid lifts slightly. If the clip is bent, bend it back gently by hand, close the jar, and repeat the side test.

When to Replace the Seal and When to Stop

Replace the seal if it is cracked, hardened, flattened, or loose in the lid groove. Replace the jar if the glass rim is chipped, if the lid is visibly distorted, or if a correctly sized new seal still leaks after you have checked the clip. Do not keep buying seals for a jar with a damaged rim — the leak will return.

If your jars are used for dry storage such as pasta, flour or dried fruit, a slow seal is a freshness issue rather than a safety one. If you are preserving or transporting liquids, treat any leak as a stop signal: use a different jar for that job until the fault is resolved.

Leak Diagnosis: Match the Symptom to the Fix

• Leaks only when tipped or laid on its side: The seal is compressing but not filling the gap. Remove it, check for flattening or hardening, and replace it with a seal sized to the jar's capacity. Seal replacement usually solves this; if it does not, check the clip pressure next.
• Leaks while standing upright: Look for a chipped or ridged glass rim or a lid that no longer sits flat. Run a fingertip around the rim and inspect the lid edge for dents. A damaged rim cannot be repaired — move that jar to dry storage or retire it.
• Seal falls out of the lid when inverted: The seal is the wrong size or has stretched. It should sit snugly in the lid groove without dropping out. Buy the seal matched to your jar's stated capacity, not the closest size you have.
• New seal still leaks after fitting: Check the clip for bending and confirm the lid sits square. If both are fine and the leak continues, the jar's rim or lid is the fault. Stop replacing seals at this point and replace the jar instead.

Parts That Solve Most Leaks

• Kilner® Replacement Seals for 0.125 Litre Clip Top Jars: Kilner 6 Replacement Rubber Seals are suitable to use with the Round Clip Top Glass Storage Jars and are sized for 0.125L jars. If your small clip top jar is the one leaking, this is the correct replacement size — buying a seal for a larger jar will not seal a 0.125L rim.
• Kilner® Set of 3 Facetted Clip Top Jars 0.95 Litre: The Kilner® Facetted Clip Top Jars feature a distinctive design reminiscent of a bygone era and are described as perfect for storing dried, preserved and pickled foods. Useful when a leaking jar is only used for dry or pickled storage, where a slow seal affects quality rather than safety, so you can keep using the jar while you source a seal.
• Kilner® Set of 3 0.5 Litre Preserve Jars: The Kilner® 0.5 litre preserve jar is described as perfect for preserving fruits, jams and sauces, with a classic clip-top design intended to ensure freshness. For liquid preserves and sauces, a leaking seal is a real problem — this is the size to check first if your leak appears during jam or sauce making.