Thermostat or other problem?

My '96 Villager has no heat and the temp guage says it's not even up to normal after driving for miles. This is a new problem since the heater worked recently. Could this be the thermostat or air somewhere? The coolant was not low but is several years old. Thanks!!!

B4 you start the car check the coolant. If its low add some. Check to see if your fans are on when you first start the car. If this all checks out normal replace the thermostat. I would also check all the fuses.