27
If the furnace fails to operate check the following:
• Is the thermostat operating properly?
• Are the blower compartment door(s) in place?
• Is the furnace disconnect closed?
• Has the circuit breaker tripped or the control board fuse
burned open?
• Is the gas turned on?
• Are any manual reset switches open?
• Is the filter dirty or plugged?
• Is the flame sensor coated? (Remove and clean with
steel wool.
(Do not use emery cloth or sandpaper!)
• Is there blockage in the condensate drain switch? Also
verify that there is no double trapping of condensate.
• Is the secondary heat exchanger free of debris and
clogs?
• Is evaporator coil clean and free of debris (If applicable).
• Are all the LED’s on the furnace control board constantly
ON? If not, refer to Table 6 or the wiring diagram (Figure
18, page 29) to determine fault condition.
IMPORTANT NOTE: The furnace will lock out after 5
failed attempts for ignition and will try again every
hour if the call for heat remains.
• If the inducer blower is operating, and items above have
been verified, check the blower limit switch and reset
if necessary. See Figure 17 for component location.
• If the furnace operates when the Blower Limit Switch is
reset, contact a qualified service technician to identify
and repair the problem.
• If the furnace still doesn’t operate, check the flame
roll-out switch (Figure 17) and reset if necessary.
• If the furnace operates when the flame rollout switch is
reset, contact a qualified service technician to identify
and repair the problem.
Diagnostic Description
Green LED Red LED
Control Fault (No Power)
Off
Off
L1/Neutral Polarity Fault
Flash
Flash
1 Hour Lockout
Alternating Flash
Normal Operation
On
On
Pressure Switch Closed Fault
On
Flash
Pressure Switch Open Fault
Flash
On
Open Limit Switch Fault
Flash
Off
Motor Fault
On
Off
Diagnostic Description
Yellow LED
Low Flame Sensor Signal
Continuous Flash
Flame Present
On
Table 6. Control Board Fault Conditions
TROUBLESHOOTING
DESCRIPTION OF COMPONENTS
The descriptions below are various functional components
that affect the operation and shutting down of this furnace.
Some of these components and their locations are shown
in Figure 17. If any component of the furnace must be
replaced, use only factory authorized replacement parts
specified in the Replacement Parts List provided online.
Blower Limit Switch:
Prevents operation when blower
is not operational.
Flame Sensor:
Verifies when a flame has carried over
from the igniter to the opposite end burner. If no flame is
detected, the furnace will shut down within 4 seconds.
Flame Roll-Out Switch:
Verifies that the burner flames
are drawn into the heat exchanger tubes. If the burner
flames are not properly drawn into the heat exchanger, the
flame roll-out switch will close the gas valve and initiate
the shutdown cycle.
Gas Valve:
Controls the flow of gas to the burners. When
the gas valve is energized it automatically opens and
regulates the gas pressure in the manifold.
Inducer Assembly:
Vents products of combustion to
the outside.
Pressure Switch:
Verifies that the inducer is drawing
the combustion gases through the heat exchanger. The
pressure switch prevents furnace operation with excessive
flue/condensate blockage or improper inducer operation.
Main Air Limit Switch:
Prevents the air temperature
leaving the furnace from exceeding the maximum allowable
outlet air temperature.
Figure 17. Furnace Components
Blower Assembly
Inducer Assembly
Gas Valve
Gas Manifold &
Burner Assembly
ON / OFF Switch
Control Board
Limit Switch
Inline Drain
Assembly
24V Transformer
Igniter
Main Air Limit Switch
Flame Sensor
Roll-Out Switch
Combustion Air Pipe
Exhaust Vent Pipe
