Fan blows but no heat

1st does your radiator have a fan shroud, if it does then replace your thermostat. If you are missing the fan shroud then install one to correct. (the fan shroud surrounds the radiator and causes the air to be pulled thru the radiator.)

Check the heater hoses; Both sides should be aprox the same temperature, if one is warm or hot, the other is cold or cooler temp, maybe have clogged heater core. Next have temp actuator checked.

seek diag as there are several issues that can cause this condition