44
T
ROUBLESHOOTING
C
HART
Symptoms of Abnormal
Operation (Legacy
& ComfortNet™
Thermostat)
Diagnostic/
Status LED
Codes
Fault Description
ComfortNet™
Thermostat Only
Possible Causes
Corrective Actions
Notes & Cautions
Message
Code
b4
MOTOR
TRIPS
b4
• Turn power OFF prior
to repair
• Furnace fails to operate.
• Integrated control
module LED display
provides b4 error code.
• ComfortNet™ thermostat
“Call for Service” icon
illuminated.
• ComfortNet™ thermostat
scrolls “Check Furnace”
message.
MOTOR LCKD
ROTOR
b5
• Turn power OFF prior
to repair.
• Replace motor with
correct replacement
part.
• Replace wheel with
correct replacement
part.
• Furnace fails to operate.
• Integrated control
module LED display
provides b6 error code.
• ComfortNet™ thermostat
“Call for Service” icon
illuminated.
• ComfortNet™ thermostat
scrolls “Check Furnace”
message.
b6
MOTOR
VOLTS
b6
• Turn power OFF prior
to repair
• Furnace fails to operate.
• Integrated control
module LED display
provides b7 error code.
• ComfortNet™ thermostat
“Call for Service” icon
illuminated.
• ComfortNet™ thermostat
scrolls “Check Furnace”
message.
b7
MOTOR
PARAMS
b7
•
• Furnace operates at
reduced performance or
• Integrated control
module LED display
provides b9 error code.
b9
LOW ID
AIRFLOW
B9
• Blocked filters.
• Restrictive ductwork.
• Undersized ductwork.
• Check filters for
blockage. Clean filters
or remove obstruction.
• Check ductwork for
blockage. Remove
obstruction. Verify all
registers are fully open.
• Verify ductwork is
appropriately sized for
system. Resize/replace
ductwork if necessary.
• Turn power OFF prior
to repair.
• Circulator blower
motor senses
high current.
• Circulator blower
motor fails to start
10 consecutive
times.
b5
• Furnace fails to operate.
• Integrated control
module LED display
provides b5 error code.
• ComfortNet™ thermostat
“Call for Service” icon
illuminated.
• ComfortNet™ thermostat
scrolls “Check Furnace”
message.
operates on low stage
when high stage is
expected.
•
Circulator blower
motor senses
a loss of rotor
control.
•
Circulator blower
motor shuts down
for over or under
voltage condition.
•
Circulator blower
motor shuts
down due to
over temperature
condition on
power module.
•
Circulator blower
motor does not
have enough
information to
operate properly.
Motor fails to start
40 consecutive
times.
•
Airflow is lower
than demanded.
•
•
•
•
•
•
