System flashing code 5 on ignition control board (ignition lockout) Reset power and burners fired up reliably on the first attempt Removed flame sensor (did not need cleaned) and cleaned it anyway Burners are crossing over ignition properly Every attempt to ignite the burners was successful Checked for loose wiring during operation to spark igniter, gas valve, control board, and flame sensor Nothing interrupted operation Tried to duplicate the fault code 5 by disconnecting the pressure switch, this trips a fault code 6 Inspected heat exchanger and filters No issues found with either Cannot find true cause for ignition lockout It could be a control board issue. Upon arrival, removed W wire at the board and it did not clear the fault the way it is supposed to. Recycling power to the unit cleared the fault. If problem persists, control board replacement may be needed System operating properly at this time