part: 29" 600 spiral tile window balance, s600-29

Thanks for posting! I'm sorry to hear you're having trouble. It sounds like your balances aren't strong enough for the weight of the sash. You mentioned the previous owners ordered the S600-29, but what color tip option did they choose? You see, the color tip option indicates the strength of the spring. If you look at the S600-29 store page, you can see a chart that tells you how much weight each option can support. I recommend weighing your sash and referring to that chart and telling me what you get.