Burnish...cleaning up contact points so they make better contact.
If you pull t-stat on inside you'll see two contacts that come together when the spring moves them. When the contacts come together they conduct elec. Those contacts get pitted from time to time. I carry a some wet dry sand paper that cleans up any contact points that might be messing up or spring (get ready for another Rving summer) I just stick sandpaper between points and hold points together and pull to get them making good contact again. Here is an example, not t-stats but you get idea. Makes contacts better for contact
http://jukeboxwiz.com/how-to-burnish-contact-points/