Furnace lockout results when a furnace is unable to achieve ignition after three attempts during a single call for heat. It is characterized by a non-functioning furnace and a one flash diagnostic LED code. If the furnace is in "lockout", it will (or can be) reset in any of the following ways.. Furnace flashing red 8 times for "external lockout". Resetting the furnace and it turns on, no issues with gas and flame, heats up the house and then. goes into lockout again. Before going into lockout, one red LED flash - indicates "flame sensed when no flame should be present" Manual suggests cleaning or replacing the flame sensor.
LED blinks on and off - System lockout; LED blinks once, stays on for a time, then blinks once more - The system cannot detect any signal from the thermostat; LED blinks twice - Problem with draft blower; LED blinks three times - The system detects a pressure switch that is still open; LED blinks four times - System detects an open.. What Is a Furnace Ignition Lockout Fault? A furnace ignition lockout fault is a safety feature present in most modern furnaces. When the furnace attempts to ignite its burner multiple times without success, the control board will lock out the ignition system to prevent potential gas buildup and unsafe conditions. Furnace Ignition Lockout Fault Code