Standard Gas Furnace Diagnostic Codes

Does not include Modulating, LXE, or Two Stage furnaces.

1 Blink = Soft Lockout (1 hour)

2 Blinks = Pressure Switch Failure (remains open)

3 Blinks = Limit Switch Open

4 Blinks = Pressure Switch Failure (remains closed)

5 Blinks = Twinning Circuit Failure *

*Only applies to boards with twinning feature.

** The National Service Department has found that the 5 Blink code can occur in some situations when an electronic thermostat is used.