Why wont finches use my bird feeder?!?

I bought a Thistle Finch Screen bird Feeder about a week ago at petco. It was not a very cheap bird feeder. I also bought thistle seed. When i got home, i cleaned my bird feeder and filled it with thistle seed. I hung the feeder on my house gutter where i can watch them eat. It has been a week and not even one finch touched my feeder! I have another tube feeder filled with a different kind of seed also placed on my gutter and sparrows go crazy for it! Just the other day i had my window open and a finch perched on the window, but then flew away. I know finches are shy birds but the sparrows use my other bird feeder like their is no tomorrow. Please help me. I live in Chicago and right now it is summer and temperatures reach up to 111 degrees. thank you!