Cadet M 411 thermostats suck! I have them throughout my home and have had problems for years with some staying on all the time, etc. I say replace them all, but good luck - the wiring is odd as the old cadet m 411 has three wires coming off it - all replacement stats have either two or four wires and there does not seem to be an easy answer as to how to properly wire the damn things. If I sound frustrated, it is because I am experiencing this as we speak, after hours of course, and have no way to complete the task at hand. I'll call a Pro tomorrow!
It is pretty bad that Cadet has not kept information about the wiring specs for the M 411 on their site. It sure would help us upgrade our systems!!!!!