Westinghouse L1RA 090N 12-B powers up and fan blows but, Only sometimes will actually heat. I have changed the filter and cleaned the flame sensor. There is a very small hairline crack in the ignitor. Could this cause my problem

Yes

Yes it could, but we need to know more about your situation. Does the glow plug glow every time there is a call for heat? Either way, I agree with wmproop. If there is a crack in the glow plug, change it out and see what happens.

I've done some more research and finally found the diagnostic codes. It indicates that the pressure switch is open with inducer on. However when I press the burner roll out reset the light stops flashing at least temporarily and the heater may or may not fire up?!