Why does my honda Civic heater just blows somewhat warm air?

I have a 98Civic Lx and the heater use to work great about a month ago it use to blow hot air to when it would be to hot but now it just blows warm air but mostly cold what can be the problem, the fuses are good!

Hi chances are the heater matrix has a leak so as it costs an absolute fortune to replace it the car usually ends up being scrapped.

Check the coolant level.
Check for debris in the heater air intake.

Coolant level could be low

Thermostat may be stuck open.