if you do not see an error, (blinking lights, code etc. ) and your heat light is on, you may have a bad heater. also check if you have a mechanical hi limit switch, it migh be popped!
to check the heater you may need a multimeter or even an Amp clamp. check voltage to heater, if 120 or 240 VAc depending on the system, then it's providing power, then it might be the heater. if cero amps, defenetly bad heater. good luck.