Help wiring thermostat for heat pump
Some of these thermostats do not require and do not give you a place for the common,blue wire.  We call these thermostats power robbing thermostats.  They have the ability to take enough power from the working wires to maintain their own functions without a common lead.  This thermostat will work just fine without the common.  Just cap it off and push it in behind the thermostat. The only drawback for this type of stat is that when you loose power to the house the stat won't work.  Who cares! Nothing else works either.