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T
ROUBLESHOOTING
C
HART
57
ComfortNet™
Thermostat Only
Symptoms of Abnormal Operation
(Legacy & ComfortNet™ Thermostat)
Diagnostic/Status
LED Codes
Fault Description
Message Code
Possible Causes Corrective Actions Notes & Cautions
x Furnace fails to operate.
x Integrated control module LED display
provides b
4
error code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls “Check
Furnace” message.
b4
x Circulator blower motor
senses a loss of rotor
control.
x Circulator blower motor
senses high current.
MOTOR
TRIPS
b4
x Abnormal motor loading, sudden
change in speed or torque, sudden
blockage of furnace air inlet or
outlet.
x High loading conditions, blocked
filters, very restrictive ductwork,
blockage of furnace air inlet or
outlet.
x Check filters, filter
grills/registers, duct system, and
furnace air inlet/outlet for
blockages.
x Turn power OFF prior to
repair.
x Furnace fails to operate.
x Integrated control module LED display
provides b
5
error code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls “Check
Furnace” message.
b5
x Circulator blower motor
fails to start 10
consecutive times.
MTR LCKD
ROTOR
b5
x Obstruction in circulator blower
housing.
x Seized circulator blower motor
bearings.
x Failed circulator blower motor.
x Check circulator blower for
obstructions. Remove and
repair/replace wheel/motor if
necessary.
x Check circulator blower motor
shaft rotation and motor.
Replace motor if necessary.
x Turn power OFF prior to
repair
x Replace motor with correct
replacement part.
x Replace wheel with correct
replacement part.
x Furnace fails to operate.
x Integrated control module LED display
provides b
6
error code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls “Check
Furnace” message.
b6
x Circulator blower motor
shuts down for over or
under voltage condition.
x Circulator blower motor
shuts down due to over
temperature condition on
power module.
MOTOR
VOLTS
b6
x High AC line voltage to furnace.
x Low AC line voltage to furnace.
x High ambient temperatures.
x Check power to furnace. Verify
line voltage to furnace is within
the range specified on the
furnace rating plate.
x See "Product Description" and
"Location Requirements &
Considerations" for furnace
installation requirements.
x Turn power OFF prior to
repair.
x Furnace fails to operate.
x Integrated control module LED display
provides b
7
error code.
x ComfortNet™ thermostat “Call for
Service” icon illuminated.
x ComfortNet™ thermostat scrolls “Check
Furnace” message.
b7
x Circulator blower motor
does not have enough
information to operate
properly.
x Motor fails to start 40
consecutive times.
MOTOR
PARAMS
b7
x Error with integrated control
module.
x Motor has a locked rotor
condition.
x Check integrated control module.
Verify control is populated with
correct shared data set. See data
errors above for details.
x Check for locked rotor condition
(see error code above for
details).
x Turn power OFF prior to
repair.
x Replace with correct
replacement part(s).
x Use memory card for the
specific model.
x Furnace operates at reduced performance
or operates on low stage when high stage is
expected.
x Integrated control module LED display
provides b
9
error code.
b9
x Airflow is lower than
demanded.
LOW ID
AIRFLOW
b9
x Blocked filters.
x Restrictive ductwork.
x Undersized ductwork.
x Check filters for blockage.
Clean filters or remove
obstruction.
x Check ductwork for blockage.
Remove obstruction. Verify all
registers are fully open.
x Verify ductwork is appropriately
sized for system. Resize/replace
ductwork if necessary.
x Turn power OFF prior to
repair.