First we replaced the thermostat. Then we replaced the ingiter. Still only blows cold air? Any one know what the problem is? :confused

Did you check the limit switches,, most of the time there is 2, connected to or close to where the burners fire up little round button like, with two wires going to them,, most have a reset button between where the wires connect,, does the inducer motor come on,or igniter light up?
Also many have a automotive type fuse in the circuit board,, also does it have a light that is flashing on the circuit board,, it won`t burn or flash with the door switch not pushed in,, let us know