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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 pressure
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?
Clear vent and/or
air intake
termination
High Gas Pressure Tripped?
High gas pressure
switch (C6097B,
N/C) set to 14” w.c.
Check incoming
gas pressure and
reset high gas
pressure switch
Low Gas Pressure Tripped?
Low gas pressure
switch (C6097A,
N/O) set to 3” w.c.
Check incoming
gas pressure and
reset low gas
pressure switch
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?
Replace blocked flue switch
(P/N: 8021205256)
Clear vent and/or air
intake termination
Remove flame sensor and
clean if necessary
Is Flame sensor plug
secure?
Fasten flame sensor plug securely to flame
sensor wire and check for corrosion deposits at
wire terminals
Check continuity of flame
sensor wire from flame
sensor to ignition control, FS
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