The following simple checks may save you a service call:

• Is the thermostat set above room temperature? (For Heating)
• Is the thermostat set below room temperature? (For Cooling)
• Is the electrical power supply on?
  • Switch mounted on furnace or air handler
  • Red cover plated emergency switch
  • Circuit breakers or fuses for indoor furnace/air handler or outside condensing unit.
• Is the blower access door firmly in place?
• Is the manual and automatic gas/oil valve open?
• Is the oil tank empty?
• Is the air filter clean?
• Are the supply and return air grills open and unobstructed?