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Sounds like a bad igniter. Remove it and check it for any defects no matter how small. Any flaw at all is reason to replace it. A little white powder is OK. Don't touch the surface of the igniter with your bare fingers. Hold it by the ceramic insulator
If the burner doesn't fire up the unit will shutdown after several ignition attempts. Your last comment would seem to imply it did actually fire up at some point.
You can't light the burner manually as a solution. You first need to address the ignition issue which is likely caused by a bad igniter based on what you describe. If the igniter has a flaw you need replace it. Only after if fires up as it should can you determine if there are any other issues.
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