Thank you for using just answer.
This heater system dont use much to give you heat. The first thing to check is coolant. Make sure you are not loosing any. Loss of coolant will result in no heat. Make sure your the top and lower radiator hoses are warm. If the top is then your thermostat is working. If the lower is hot then the radiator is not stopped up. If all is good then you may have a bad or clogged heater core. See if both hoses are hot. If not flush if still dont work replace the heater core.