Heater on 2003 Chevrolet Impala

The heater will not blow hot air. What could be the problem?

Asked by for the 2003 Chevrolet Impala
Often times when a heater will not work, it is a basic problem like low coolant or a stuck heater control valve. Don't assume something with out checking. often a heater core problem will cause the windows to really fog up and there will be coolant on the floor mat like you say above.
Thank you so much for answering my question. The car was low on water. as soon as we added coolant the heater started working. The water in the floor seems to be coming from a blocked drain under the dash at the firewall. I don't really know what im looking for to fix it but at least it has heat. You were so helpful!!! Thanks to everyone that responded.
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Heater core