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Do you have 24 VAC at the gas valve when the burner won't light? Does is sometimes light?
You need to test for 24 v at the gas valve when it doesn't fire up and the ignitor is glowing . If you have 24 v and no ignition then you have a bad gas valve. If you don't have 24v at the valve then you either have a bad board (IFC) or a bad connection between the board and the valve.
What you're looking for doesn't exist. I outlined the tests you need to perform. If I didn't provide enough added detail, more than the troubleshooting guide I can't help that. Whether you rate or not is up to you.