I have had an old control device in our new home for many years. And for some reason I just never got rid of this thing. It was a single of those plastic control units on the wall with a slider that was plastic. When the old plastic control device to our central heating and a/c finally broke down it was not a pretty thing! It was the dead freezing of the Winter. And I had our heating on. Well, when I went to adjust the control device on the wall the slider broke off. And then what happened was our control device was stuck pumping out all of this heating! It was so awful it nearly boiling the house. I had to go down to our basement and pull the fuse on the circuit that ran the central heating and a/c unit. That was the only way to get our central heating and a/c device to finally shut down! I then opened many windows and doors in the house, and this cooled everything down. When I called the local heating and a/c corporation, the certified heating and a/c specialist was kind of shocked that I still had a single of these old slider plastic control units. He provided to sell me either a digital control device and a programmable smart control unit. I chose to go with a smart programmable control unit. I had heard so much about these things in terms of saving on energy use that I really wanted to try a single out!