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1 flash is ignition failure. Does the igniter glow? do the burners fire up then go out?
Ok, you need to check for 24 vac at the gas valve while the igniter is glowing. If you have 24 v at the valve leads and the burners don't fire up then you have a faulty gas valve. If you don't have 24 v then you either have a bad board or a bad connection between the board and the gas valve. I'm assuming you have adequate gas pressure at the gas valve inlet.
Cycle the power off, wait a couple minutes then cycle it back on to try and clear a hard lockout. This will only works with a few errors but a 1 error is one that should work. With a soft lockout the unit will retry on its own after a period of time usually 1 hour. One thing you can do for PM is to clean the flame sensor rod with steel wool. Also change the filters every couple months depending on how dirty they get