You may be able to fix the springs in the thermostat, but it will only be temporary. Our Comfort Center got to the point where it was almost impossible to change the temperature, so we just last week replaced the system with the 5 button Comfort Center and the two control boards. Total cost installed was $567.
FMCA had an article on how to fix the springs, but I don't have a URL for it. A search of their magazine back issues may turn it up.