Thermotite window won't stay up

Sounds like an issue with the balance. Based on your tilt shoe, which resembles the 15-087 from what I can see, you might have the Series 180 coil spring. All you would need to do is replace these and your window should stay up again. I'm just not sure which Series 180 you have, or if that is even what you need. I recommend removing your hardware from the window and carefully comparing it to the dimensions and pictures on our site. That's the only way to be sure.