I have an HQ16. I used to have this problem until I (accidentally) stumbled on the solution for my machine. You may want to try this to see if it solves your problem. Thread the machine, then pull the thread through the top tension disks so they are secure. To make it secure, I grab the thread above the disk with one hand and then below the disk with another hand and pull the thread toward me and move it up and down between the disk a couple of times, thus securing it in the disk. Hope this helps.