The first thing with any boiler that has stopped working is to make sure there's water pressure in the system. Should be anywhere from 10 to 20psi (+/-).
If there is water pressure, AND gas in the tank, go ahead and hit the reset button on the control module and see what happens. If it fails again, refer to the troubleshooting chart on the document I provided a link to. I looked, but didn't see any "F" error code; should be "F" plus a two-digit number.
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