Here are some common reasons why a heater may blow cool air:
Some heaters have a fan only setting which will enable the user to use the heater as a fan. If your model has that feature, check to see if the heater is on the fan only setting.
If the heater is on one of the heat settings, rather than the fan only setting, then it may have overheated and shut off power to the heater. Follow the reset instructions found on the heater or in the owners manual.
With some digital thermostats, the fan will run for 30 seconds without heat once the set temperature is reached. This is to blow out excess heat and ensure an accurate and consistent temperature reading.
If the heater continues to blow cool air after checking the above suggestions, please contact customer support.