Hi, welcome to Just answer
How old is this unit ?
Have you tried to thread the top part, if not then you’ll need to pull the thread back and forth in the top thread guide and check the tail in front is not curly. If still the issue persists, then it means that the machine has a bad thread sensor on it and needs to be replaced.
You can also try to Turn the machine off. Put the needle in the lowest position. Turn the machine on. ... If this wont solve the problem then you will have to contact your Janome dealer to get the board checked
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