I need to know what is the problem with the thermastat when on heat the unit does not heat up when put on auto. I also need to know where to purchase a new thermastat to replace this one. Thanks merced gonzalez

I need to know what is the problem with the thermastat when on heat the unit does not heat up when put on auto. I also need to know where to purchase a new thermastat to replace this one. thanks merced gonzalez

Thisn thermastat operates an electric system at a module home for kids school