Your thermostat can be configured for multiple system types. The EMER position is reserved for a multi-stage heat pump system. If you have a gas/electric furnace the EMER mode is not available and will display NO if you try and select it. If you have a multi-stage heat pump system and is still says NO then your thermostat is configured for the wrong system type. Please see the user manual for information on changing the system type. All users manuals are available on this web site.