Code 12 (dot-dash-dash or short-long-long) means "Blower on after power up (115V or 24 V)" - Normal operation. Blower runs for the selected blower off delay if unit is powered up during a call for heat (R-W/W1 closed) or when blower on period is activated (R-W/W1 opens).
Does the flash ever stop (LED always on) and does the blower ever stop? If the answer to both questions is yes, then there's nothing wrong with the furnace. You may also reset power (turn off, wait 20 seconds, turn on) to the unit to reset the controller and see if it starts without a status code next time.