2004 Honda Accord heater issue

The first thing I would check for is air in the system, here is a video on how to bleed the cooling system. DON’T WORRY IF YOU DON’T HAVE A BLEEDER VALVE FOR THE COOLING SYSTEM IT’S ONLY THERE TO HELP FILL THE SYSTEM FASTER. If you don’t find air in the system it’s time to see if the engine is coming up to temperature, if your temperature gauge reads low then you MIGHT have a problem with the thermostat, if you suspect this replace it with an OE unit. If all of this is good then check the heater control valve located in the heater hose going into the firewall, have someone move the temp from hot to cold while the engine is running and you observe the lever on the valve, it should have a full sweep if not there may be a problem with this valve OR it’s controls. Lastly it could be a problem with the HVAC blend doors that is a different issue altogether but lets cross that bridge should we come to it, bleeding the system is the first priority.

http://www.youtube.com/watch?v=zUpXgAJ1gjU