A. Failure of lids to seal may be caused by one or more of the following:
•A chip on the rim of the jar.
•Failure to follow manufacturer's directions for preparing flats.
•Presence of food particles on jar rim. Always wipe rim clean before putting on lids. I use white vinegar to wipe my rims with as this removes any sticky substances from the syrup or broths/gravies etc.
•Leaving too little headspace, letting pressure in pressure canner fluctuate, or lowering the pressure too suddenly. In all of these cases, food particles may be forced between the jar and lid, causing sealing failure.
•Leaving too much headspace may prevent sealing because the processing time was not long enough to exhaust all the air from the inside of the jar.
•Not removing air bubbles can have the same effect as leaving too much headspace.
•Putting screw bands on too tightly.
•Tightening screw bands after removing jars from canner or the preserving unit.
•Reusing lids.(It is recommended that you Use flat metal lids only once).
•Using commercial or one-trip jars, such as for mayonnaise, peanut butter, or baby food. These jars have slightly different sizes of sealing edges and are not recommended for home canning/preserving.
However there is no reason that you are not able to resuse these types of jars providing you use new lids. New lids can be purchased quite easily and fairly inexpensively.