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This type of failure indicates a flame rectification signal issue through the flame rod.
Fault =
“AIR FLOW FAIL”
This error can indicate a blocked flue or blocked intake condition, low gas pressure switch tripped (optional) or high gas pr essure
switch tripped (optional). To identify the safety that is open set the multimeter to Vac and measure the voltage from one contact to
ground. The contacts produce a 24Vac when the circuit is closed.
Is vent and/or air intake
blocked?
YES
Clear vent and/or
air intake
termination
NO
High Gas Pressure Tripped?
YES
High gas pressure
switch (C6097B,
N/C) set to 14” w.c.
NO
YES
Check incoming
gas pressure and
reset high gas
pressure switch
Low Gas Pressure Tripped?
YES
Low gas pressure
switch (C6097A,
N/O) set to 3” w.c.
YES
Check incoming
gas pressure and
reset low gas
pressure switch
NO
Turn blocked flue switch set
screw 1-2 turns clockwise,
until burner stays on at high
fire
Is Blocked flue switch (N/C)
closed when fan is not turning?
NO
Replace blocked flue switch
(P/N: 8021205256)
YES
Clear vent and/or air
intake termination
Remove flame sensor and
clean if necessary
NO
Is Flame sensor plug
secure?
NO
Fasten flame sensor plug securely to flame
sensor wire and check for corrosion deposits at
wire terminals
YES
Check continuity of flame
sensor wire from flame
sensor to ignition control, FS
NO
YES
Replace flame sensor and graphite flame sensor
gasket
Replace sensor wire since corrosion can affect
the perceived flame signal significantly and
position it away from the heat exchanger
