Heater blowing cold air only

My 2000 Ford Explorer is only blowing cold air from the heater. Sometimes after driving for 30 minutes it might blow some warm air. The temperature gauge is very slow to rise also. Any help will be greatly appreciated!

Have you replaced the thermostat? Sounds like a thermostat to me.

Thanks for the reply, I thought it might be the thermostat too. Turns out it was a heater control vacuum valve that was stuck closed. Got it replaced and I'm warm again!!! :smokin:

THats the other part I was thinking of if the thermostat didn't work.