The existing Potterton room stat has stopped working, and when the radiators come on they are boiling hot.So when I\\\'ve gone to replace the stat, I\\\'ve noticed that the existing one , as well as live & neutral, has a H for heating, which my replacement does not have, it just has a terminal for L & N, the three, numbered 1,2 & 3. Do I need to replace the stat with a Potterton like for like ?