My Janome 6500 is on its third foot pedal. Or maybe 4th, I'm not sure. The machine is about 3.5 years old. It's definitely the pedal itself, not because it's stuck under anything, at least in my situation. The service guy has witnessed it himself, which is fortunate for me because I haven't had to pay for a replacement foot. I have, however, marked the bottom of the pedal with a Sharpie so I don't get the old one back someday! If you don't replace the foot, the machine will eventually begin sewing whenever you lower the presser foot, and if you raise it again, the machine will probably start beeping at you to lower it so it can start stitching again. It's a little unnerving, but you have to admit, it makes a good story, especially when you can tell your friends that your machine sews even when you're across the room pressing the last seam. If only you could train it to sew the next seam the right way while you're pressing... (sigh...)
This problem has come up here before. I would suggest that you find the previous postings, and if you can't get some satisfaction from your service person, contact Janome directly and present the evidence to them.