The bobbin thread does not catch - the material feeds through, the needle works, the top stitch looks good, but there is no thread holding it together on the bottom.
Hello Laura,
The most common cause is a new needle being put in the wrong way round, or, the needle is blunt or bent, the very worst it can be is the machine is out of time but I would definitely try the needle first, get back if you want to.
Ken
drivewithken@blueyonder.co.uk