Hotpoint tumble dryer tdc60?

What is the difference between the two thermostats on a hotpoint tumble dryer,one has a green spot on it,i recently changed both stats as the one with the green dot had no continuity,I put it back together and it worked fine,now after two weeks it has stopped heating so I checked the stats again and the one with the green spot had no continuity so I put the old one without the green spot in and now it works fine,was just wondering is this safe and what does the one with the green spot do,many thanks for any advice.