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Carrier gas furnace code 23.5: High pressure switch stuck closed
Gas furnace, Canada and United States
The high (secondary) pressure switch is closed when it should be open, so the control will not start heating.
This needs a licensed gas technician. There is nothing safe to check yourself. Leave the covers on and book a professional.
This involves the flue or exhaust. A blocked or leaking flue can let carbon monoxide into the home.
Only some models show this code. Check the list below.
What causes it
-
Blocked pressure tubing holding the switch closed.
-
A pressure switch stuck closed.
How to read this code on your unit
The three-digit display sits on the furnace control behind the blower door. Through the sight glass in the door you see only the status light, which flashes the first two digits of the code. 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 a 33.x code. Write down what you see before you open the door or switch the furnace off. The full code with its third digit shows on the control display only with the door removed and the door switch closed, which is a job for a technician. A technician can also look back at the last 7 faults in the FLt menu. Stored codes are erased by themselves after 72 hours of powered operation after the last fault, and the display shows non when no fault is stored.
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
62 models in 7 ranges
| Range | Models |
|---|---|
| 58TN0B/58TN1B | 58TN0B045C17-12, 58TN0B070C14-12, 58TN0B070C17-16, 58TN0B070C21-20, 58TN0B090C17-16, 58TN0B090C21-20, 58TN0B110C21-20, 58TN0B135C24-22, 58TN1B045C17-12, 58TN1B070C14-12, 58TN1B070C17-16, 58TN1B070C21-20, 58TN1B090C17-16, 58TN1B090C21-20, 58TN1B110C21-20, 58TN1B135C24-22 |
| 58TP0B/58TP1B | 58TP0B045V14-12, 58TP0B070V14-12, 58TP0B070V17-16, 58TP0B090V17-16, 58TP0B090V21-20, 58TP0B110V21-22, 58TP0B135V24-22, 58TP1B045V14-12, 58TP1B070V14-12, 58TP1B070V17-16, 58TP1B090V17-16, 58TP1B090V21-20, 58TP1B110V21-22, 58TP1B135V24-22 |
| 59TN6C | 59TN6C040C14-10, 59TN6C060C17-14, 59TN6C080C17-14, 59TN6C080C21-20, 59TN6C100C21-22, 59TN6C120C24-22 |
| 59TN7A | 59TN7A060C17-16, 59TN7A080C17-16, 59TN7A080C21-20, 59TN7A100C21-22, 59TN7A120C24-22 |
| 59TP6C | 59TP6C040V14-10, 59TP6C040V17-12, 59TP6C060V14-12, 59TP6C060V17-16, 59TP6C080V17-16, 59TP6C080V21-20, 59TP6C100V21-20, 59TP6C100V21-22, 59TP6C120V24-22 |
| 59TP7A | 59TP7A060V17-16, 59TP7A080V17-16, 59TP7A080V21-20, 59TP7A100V21-20, 59TP7A100V21-22, 59TP7A120V24-22 |
| 59MN7C | 59MN7C060C17-14, 59MN7C060C21-20, 59MN7C080C17-14, 59MN7C080C21-20, 59MN7C100C21-22, 59MN7C120C24-22 |
Where this comes from
- 59TP6C gas furnace, installation, start-up, operating and service instructions (59TP6C-03SI) , page 56, 77
- 59TN6C gas furnace, installation, start-up, operating and service instructions (59TN6C-04SI) , page 57, 77
- 59MN7C gas furnace, installation, start-up, operating and service instructions (59MN7C-04SI) , page 53, 75
Checked against the manufacturer's manual on 11 October 2026.
Other Carrier gas furnace codes
| Code | Meaning | What you can do |
|---|---|---|
| 23 | Flue or venting fault (depends on model) | Call a pro |
| 43 | Lower pressure switch open while a higher one is closed | Call a pro |
| 14.4 | Lockout after repeated pressure switch openings | Safe checks first, then a pro |
| 23.1 | Flue or venting fault (depends on model) | Call a pro |
| 23.2 | Secondary pressure switch stuck closed | Call a pro |
| 23.3 | Pressure transducer senses over-pressure | Call a pro |
| 23.4 | Low pressure switch stuck closed | Call a pro |
| 23.6 | Medium pressure switch stuck closed | Call a pro |
| 31.1 | Flue or venting fault (depends on model) | Depends on your model |
| 31.2 | Flue or venting fault (depends on model) | Depends on your model |
| 31.3 | Secondary pressure switch lockout after 3 failed trials | Safe checks first, then a pro |
| 31.4 | Loss of pressure before the blower started | Safe checks first, then a pro |
See all flue or venting fault codes on gas furnaces across brands.