A tip on how to find out if it is a Normally closed (N/C) switch or a Normally open switch(N/O) IF YOU CAN READ THE #’s on the switch. The first thing you need to do is READ THE OWNERS MANUAL If you dont have one most manufactures have them available on their website. MOST BRAND there will be a F in front of the Temperature rating on most N/O Fan limit switches (waits for the switch to heat up to a set temperature before it gives power to the component) Also called a Low limit switch. F120-10 switch works like this the contacts will close at 120 deg. allowing power to flow threw the switch. the 10 after the 120 is after a 10 deg cool down the switch will OPEN and NOT alow power to flow threw the switch at 110 deg. http://www.hearthtools.com/parts/100-00231.jpg Most manufactures have updated to a ceramic switch like http://www.hearthtools.com/parts/lowlimit.jpg MOST BRAND there will be a L in front of the Temperature rating on most N/C Fan limit switches (waits for the switch to heat up to a set temperature before it CUTS power to the componentS) Also called a High limit switch. L200-40 switch works like this the contacts will OPEN at 200 deg. NOT allowing power to flow threw the switch. the 40 after the 200 is after a 40 deg cool down the switch will CLOSE and ALLOW power to flow threw the switch at 160 deg. This kind of switch is called a HIGH limit switch and most times is a safety for if a stove over heats. it will shut down the Component(S) connected to it. http://www.hearthtools.com/parts/100-00233.jpg Some manufactures are now using a Manual Reset Type switch for the high limit (stove over heat). when the switch over heats the stove will not work until the Button on the switch is Pushed in and reset. this is a pain but I see why they do it. the switch tripped for a reason and they dont want a bone head user keep on using the if there is a problem with the stove.