R - A 7
Alert Code Response
Error 26: Temperature limit fault
Comfort Control = Err 26
User Interface = HIGH LIMIT
Furnace Fault LED = 4 Flash
Problem Description
• Open high limit switch
Possible Causes/Solutions
• Low airflow across heat exchanger
- Blocked evaporator coil
- Dirty return air filter
- Dirty blower wheel
• Outlet gas pressure set to high
Error 26: Temperature limit fault
Comfort Control = Err 26
User Interface = AUX LIMIT
Furnace Fault LED = 4 Flash
Problem Description
• Open reverse flow limit switch
Possible Causes/Solutions
• Restricted fins of secondary heat exchanger
• Blocked evaporator coil
• Blower not operating properly
Error 26: Temperature limit fault
Comfort Control = Err 26
User Interface = IND LIMIT
Furnace Fault LED = 9 Flash
Problem Description
• Open inducer limit switch
Possible Causes/Solutions
• Restricted flue assembly
• Excessive temperature rise across heat exchanger
- See furnace nameplate for acceptable range
• Faulty draft inducer motor
Error 27: Replace device
Comfort Control = Err 27
User Interface = No Alert Displayed
Air Handler Fault LED = No Fault Reported
Furnace Fault LED = No Fault Reported
Problem Description
• Internal temperature sensor within comfort control has
failed
Possible Causes/Solutions
• Replace comfort control
- Failure could be caused by voltage spikes or
electrostatic discharge
Error 34: Flame detect fault
Comfort Control = Err 34
User Interface = FLAME ERROR
Furnace Fault LED = 5 Flash
Problem Description
• Flame sensed for more than 5 seconds when no flame
should be present
Possible Causes/Solutions
• Gas valve will not close
- Debris in gas valve; no drip leg installed
• Internal failure of furnace control board
- Replace control board
Error 37: Filter configuration fault
Comfort Control = Err 37
User Interface = No Alert Displayed
Air Cleaner Fault LED = No Fault Reported
Problem Description
• Duplicate filter timers have been enabled
Possible Causes/Solutions
• ISU 500 and/or 501 on the communicating comfort
control is not set to “E” for auto-discovery
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