Hi to everyone. First time poster here.
I have a 2005 Civic EX which I have a heater problem with. Heater blows cold air even after starting and let run for an hour. Temperature gauge goes up to normal. Antifreeze is good. Heater will blow hot air after I rev the engine a few times. What could be the problem? Thanks for any help.

 

This sounds like there is not enough coolant. Check the level in the radiator itself, it should be full to the top. Do not just check the white plastic tank.

 

Coolant is good. Did fill the radiator, even jacked up the front end to make sure the radiator is full of coolant. Could it be a clogged heater coil?

 

It could, you can disconnect the heater hoses at the engine end then flush the core forward and backward with a garden hose. Dash dial must be set to full hot, engine not running of course. Also check that the valve on the firewall moves all the way when you turn the dial.