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Carrier gas furnace code 45: Control circuitry lockout
Gas furnace, Canada and United States
The furnace control found a fault in its own circuits, such as a stuck gas valve relay, a failed flame sensing circuit or a software check error. It locks out for 1 hour and then resets itself. If the code comes back after the power is reset, the control is replaced.
On the status light, this code is 4 short flashes, then 5 long flashes.
This needs a licensed gas technician. There is nothing safe to check yourself. Leave the covers on and book a professional.
This involves the gas supply or burner. Only a licensed technician should open the unit or work on gas parts.
What causes it
-
A fault on the furnace control itself. A technician resets the power to clear the lockout and replaces the control if the code repeats.
How to read this code on your unit
The amber status light (red on some older boards) on the furnace control shows through a small window in the blower access door. A steady light means the control has power and no fault to show. A code is two digits. Count the short flashes for the first digit, then the long flashes for the second, so 3 short flashes followed by 3 long flashes is code 33, and 1 short then 1 long is code 11. Write the code down before you open the door or switch the furnace off.
Booking a licensed gas technician
Book a licensed gas technicianlicensed gas technician
- Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
- Note the code, how often it appears, and the model and serial numbers from the rating label.
- Book a licensed gas technician and give them those details.
Models that show this code
328 models in 26 ranges
| Range | Models |
|---|---|
| 58CTA/CTX | 58CTA045-08, 58CTA045-12, 58CTA070-08, 58CTA070-12, 58CTA070-16, 58CTA090-14, 58CTA090-16, 58CTA090-20, 58CTA110-12, 58CTA110-16, 58CTA110-22, 58CTA135-16, 58CTA135-22, 58CTA155-20, 58CTX045-08, 58CTX045-12, 58CTX070-08, 58CTX070-12, 58CTX070-16, 58CTX090-14, 58CTX090-16, 58CTX090-20, 58CTX110-12, 58CTX110-16, 58CTX110-22, 58CTX135-16, 58CTX135-22, 58CTX155-20 |
| 58CVA/CVX | 58CVA070-12, 58CVA090-16, 58CVA110-20, 58CVA135-22, 58CVA155-22, 58CVX070-12, 58CVX090-16, 58CVX110-20, 58CVX135-22, 58CVX155-22 |
| 58DLA/DLX | 58DLA045-08, 58DLA045-12, 58DLA070-08, 58DLA070-12, 58DLA070-16, 58DLA090-14, 58DLA090-16, 58DLA090-20, 58DLA110-12, 58DLA110-16, 58DLA110-22, 58DLA135-16, 58DLA135-22, 58DLA155-20, 58DLX045-08, 58DLX045-12, 58DLX070-08, 58DLX070-12, 58DLX070-16, 58DLX090-14, 58DLX090-16, 58DLX090-20, 58DLX110-12, 58DLX110-16, 58DLX110-22, 58DLX135-16, 58DLX135-22, 58DLX155-20 |
| 58SB0A/58SB1A | 58SB0A045E14-12, 58SB0A045E17-12, 58SB0A070E14-12, 58SB0A070E17-12, 58SB0A070E17-16, 58SB0A070E21-16, 58SB0A090E17-14, 58SB0A090E21-16, 58SB0A090E21-20, 58SB0A090E24-20, 58SB0A110E21-20, 58SB0A110E24-20, 58SB0A135E24-20, 58SB0A155E24-20, 58SB1A045E14-12, 58SB1A045E17-12, 58SB1A070E14-12, 58SB1A070E17-12, 58SB1A070E17-16, 58SB1A070E21-16, 58SB1A090E17-14, 58SB1A090E21-16, 58SB1A090E21-20, 58SB1A090E24-20, 58SB1A110E21-20, 58SB1A110E24-20, 58SB1A135E24-20, 58SB1A155E24-20 |
| 58SC0A/58SC1A | 58SC0A045E14-12, 58SC0A045E17-12, 58SC0A070E14-12, 58SC0A070E17-12, 58SC0A070E17-16, 58SC0A070E21-16, 58SC0A090E17-14, 58SC0A090E21-16, 58SC0A090E21-20, 58SC0A090E24-20, 58SC0A110E21-20, 58SC0A110E24-20, 58SC0A135E24-20, 58SC1A045E14-12, 58SC1A045E17-12, 58SC1A070E14-12, 58SC1A070E17-12, 58SC1A070E17-16, 58SC1A070E21-16, 58SC1A090E17-14, 58SC1A090E21-16, 58SC1A090E21-20, 58SC1A090E24-20, 58SC1A110E21-20, 58SC1A110E24-20, 58SC1A135E24-20 |
| 58SP0A/58SP1A | 58SP0A045V14-12, 58SP0A045V17-16, 58SP0A070V17-16, 58SP0A070V21-20, 58SP0A090V21-20, 58SP0A090V24-20, 58SP0A110V24-22, 58SP1A045V14-12, 58SP1A045V17-16, 58SP1A070V17-16, 58SP1A070V21-20, 58SP1A090V21-20, 58SP1A090V24-20, 58SP1A110V24-22 |
| 58STA/STX | 58STA045-08, 58STA045-12, 58STA070-08, 58STA070-12, 58STA070-16, 58STA090-14, 58STA090-16, 58STA090-20, 58STA110-12, 58STA110-16, 58STA110-22, 58STA135-16, 58STA135-22, 58STA155-20, 58STX045-08, 58STX045-12, 58STX070-08, 58STX070-12, 58STX070-16, 58STX090-14, 58STX090-16, 58STX090-20, 58STX110-12, 58STX110-16, 58STX110-22, 58STX135-16, 58STX135-22, 58STX155-20 |
| 58TN0A/58TN1A | 58TN0A045C17-12, 58TN0A070C14-12, 58TN0A070C17-16, 58TN0A070C21-20, 58TN0A090C17-16, 58TN0A090C21-20, 58TN0A110C21-20, 58TN0A135C24-22, 58TN1A045C17-12, 58TN1A070C14-12, 58TN1A070C17-16, 58TN1A070C21-20, 58TN1A090C17-16, 58TN1A090C21-20, 58TN1A110C21-20, 58TN1A135C24-22 |
| 58TP0A/58TP1A | 58TP0A045V14-12, 58TP0A070V14-12, 58TP0A070V17-16, 58TP0A090V17-16, 58TP0A090V21-20, 58TP0A110V21-22, 58TP0A135V24-22, 58TP1A045V14-12, 58TP1A070V14-12, 58TP1A070V17-16, 58TP1A090V17-16, 58TP1A090V21-20, 58TP1A110V21-22, 58TP1A135V24-22 |
| 59MN7A | 59MN7A060V17-14, 59MN7A080V17-14, 59MN7A060V21-20, 59MN7A080V21-20, 59MN7A100V21-22, 59MN7A120V24-22 |
| 59MN7B | 59MN7B060C17-14, 59MN7B060C21-20, 59MN7B080C17-14, 59MN7B080C21-20, 59MN7B100C21-22, 59MN7B120C24-22 |
| 59SC2A, 59SC2B and 59SC2C | 59SC2A040E14-10, 59SC2A060E14-10, 59SC2A060E17-14, 59SC2A080E17-16, 59SC2A080E21-20, 59SC2A100E21-14, 59SC2A100E21-20, 59SC2A120E24-20, 59SC2B040E14-10, 59SC2B060E14-12, 59SC2B040E17-12, 59SC2B060E17-16, 59SC2B080E17-16, 59SC2B080E21-20, 59SC2B100E21-16, 59SC2B100E21-22, 59SC2B120E24-22, 59SC2C040E14-10, 59SC2C060E14-12, 59SC2C040E17-12, 59SC2C060E17-16, 59SC2C080E17-16, 59SC2C080E21-20, 59SC2C100E21-16, 59SC2C100E21-20, 59SC2C120E24-20 |
| 59SC2D | 59SC2D040E14-10, 59SC2D040E17-12, 59SC2D060E14-12, 59SC2D060E17-14, 59SC2D080E17-16, 59SC2D080E21-20, 59SC2D100E21-20, 59SC2D100E21-22, 59SC2D120E24-20 |
| 59SC5A | 59SC5A026E14-08, 59SC5A040E14-10, 59SC5A060E14-10, 59SC5A040E17-12, 59SC5A060E17-14, 59SC5A080E17-16, 59SC5A080E21-20, 59SC5A100E21-14, 59SC5A100E21-20, 59SC5A120E24-20, 59SC5A140E24-20 |
| 59SC5B | 59SC5B026E14-10, 59SC5B040E14-10, 59SC5B040E17-12, 59SC5B060E14-12, 59SC5B060E17-16, 59SC5B080E17-16, 59SC5B080E21-20, 59SC5B100E21-20, 59SC5B100E21-22, 59SC5B120E24-22, 59SC5B140E24-22 |
| 59SP5A | 59SP5A026E14-10, 59SP5A040E14-10, 59SP5A060E14-12, 59SP5A040E17-12, 59SP5A060E17-14, 59SP5A080E17-16, 59SP5A080E21-20, 59SP5A100E21-20, 59SP5A120E24-22 |
| 59SP6A | 59SP6A040V14-10, 59SP6A040V17-12, 59SP6A060V14-12, 59SP6A060V17-14, 59SP6A080V17-16, 59SP6A080V21-20, 59SP6A100V21-20, 59SP6A120V24-22 |
| 59TN6A | 59TN6A060V17-14, 59TN6A080V17-14, 59TN6A080V21-20, 59TN6A100V21-22, 59TN6A120V24-22 |
| 59TN6B | 59TN6B060C17-14, 59TN6B080C17-14, 59TN6B080C21-20, 59TN6B100C21-22, 59TN6B120C24-22 |
| 59TP5A | 59TP5A040E14-10, 59TP5A060E14-12, 59TP5A040E17-12, 59TP5A060E17-14, 59TP5A080E17-16, 59TP5A080E21-20, 59TP5A100E21-20, 59TP5A120E24-22 |
| 59TP6A | 59TP6A040V14-10, 59TP6A040V14-12, 59TP6A060V17-12, 59TP6A060V17-14, 59TP6A080V17-16, 59TP6A080V21-20, 59TP6A100V21-20, 59TP6A120V24-22 |
| 59TP6B | 59TP6B040V14-10, 59TP6B040V17-12, 59TP6B060V14-12, 59TP6B060V17-14, 59TP6B080V17-16, 59TP6B080V21-20, 59TP6B100V21-20, 59TP6B120V24-22 |
| 58CU0A | 58CU0A040C17-12, 58CU0A060C17-16, 58CU0A080C21-20, 58CU0A100C21-20 |
| 58SU0A | 58SU0A040E17-12, 58SU0A060E17-16, 58SU0A080E21-20, 58SU0A100E21-20 |
| 59CU5A | 59CU5A060C17-16, 59CU5A080C21-20, 59CU5A100C21-22 |
| 59SU5A | 59SU5A040E17-12, 59SU5A060E17-16, 59SU5A080E21-20, 59SU5A100E21-20, 59SU5A100E21-22 |
Where this comes from
- 59SC5A single-stage condensing gas furnace, installation, start-up, operating and service instructions (59SC5A-13SI) , page 67, 83
- 58STA/STX single-stage induced-combustion gas furnace, installation, start-up, operating and service instructions (58ST-24SI) , page 43
- 59TP6A two-stage variable-speed condensing gas furnace, installation, start-up, operating and service instructions (59TP6A-10SI) , page 90
- 58SU0A 80% single-stage ultra-low NOx gas furnace, installation, start-up, operating and service instructions (58SU0A-06SI) , page 33
- 59SU5A single-stage ultra-low NOx condensing gas furnace, installation, start-up, operating and service instructions (59SU5A-05SI) , page 51
- 59CU5A single-stage communicating ultra-low NOx condensing gas furnace, installation, start-up, operating and service instructions (59CU5A-01SI) , page 65
Checked against the manufacturer's manual on 11 October 2026.
Other Carrier gas furnace codes
| Code | Meaning | What you can do |
|---|---|---|
| 35 | Modulating gas valve not communicating | Call a pro |
| 41 | Blower motor fault, speed or communication lost | Call a pro |
| 42 | Inducer motor fault | Safe checks first, then a pro |
| 43 | Lower pressure switch open while a higher one is closed | Call a pro |
| 10.1 | Line voltage polarity reversed | Call a pro |
| 10.2 | Refrigerant leak detected, dissipation active | Call a pro |
| 13.1 | Limit circuit lockout, a limit or rollout switch stayed open | Safe checks first, then a pro |
| 14.1 | Ignition lockout after repeated failed lighting attempts | Safe checks first, then a pro |
| 45.1 | Internal control fault | Call a pro |
| 45.2 | Gas valve relay will not close | Call a pro |
| 45.3 | Control memory (EEPROM) fault | Call a pro |
| 45.4 | Microprocessor communication lost | Call a pro |
See all control board fault codes on gas furnaces across brands.