2004 honda accord heater not working?

2004 honda accord ex 2.4 heater doesn't get warm at all what could it be? What should I replace?

Does the blower work? Check the coolant level. Idle the engine and check if the engine temp is increasing and goes to mid-level after a while. If not, replace the thermostat. If the engine temp is ok, flush the heater core and check if the heater valve (if there's one) is working. Still no heat, check for a bad blend door/motor.

Almost certainly the air flap as the heater core is constantly hot on modern cars, feel the hose going into the bulkhead it should be hot

Yes, dashboard would be taken away to repair the air-con/heater system… Cost maybe within $2000~$4000 for factory accessory (depends on what is out of service)

Check the coolant level in the radiator first. Sounds like you have a leak.

Yes

Things to check. Coolant level in the radiator. Radiator hoses and coolant hoses, ( they could be soft and collapsing when hot ). The thermostat may be stuck open, and needs to be replaced. Have a knowledgeable friend that's mechanically inclined, check these easy 'fixes' before taking it to a mechanic that needs to be paid for these services.

Coolant level. Make sure that that is up… Otherwise no hot coolant gets to the heater core… Is the first thing I would check for. Then check the heater hose gate to be sure it works(have somebody turn it from cold to hot and you should see something move in the engine compartment. This is a maybe. Otherwise let a mechanic take a look.