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Carrier gas furnace code 26.1: Burner thermal switch open, permanent lockout
Gas furnace, Canada and United States
The burner thermal switch (BTS) is open. If it opens during a call for heat the control locks out permanently, and only switching the power off and on clears it.
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.
Only some models show this code. Check the list below.
What causes it
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A blocked burner inlet or burner mesh.
-
A power loss during heating that opened the switch.
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The manifold pressure or gas firing rate set wrongly.
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 4 long flashes is a 34.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, 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
13 models in 3 ranges
Where this comes from
- 58SU0B gas furnace, installation, start-up, operating and service instructions (58SU0B-03SI) , page 24, 40
- 59SU5B gas furnace, installation, start-up, operating and service instructions (59SU5B-03SI) , page 48, 64
- 58CU0B gas furnace, installation, start-up, operating and service instructions (58CU0B-03SI) , page 28, 44
Checked against the manufacturer's manual on 11 October 2026.
Other Carrier gas furnace codes
| Code | Meaning | What you can do |
|---|---|---|
| 13 | Limit circuit lockout (depends on model) | Safe checks first, then a pro |
| 26 | Burner thermal switch open | Call a pro |
| 33 | Limit circuit fault, a limit or rollout switch is open | Safe checks first, then a pro |
| 13.1 | Limit circuit lockout, a limit or rollout switch stayed open | Safe checks first, then a pro |
| 25.5 | Installer settings are corrupted | Call a pro |
| 25.6 | Wrong program loaded for this control | Call a pro |
| 25.7 | Non-condensing program in a condensing furnace | Call a pro |
| 26.2 | Burner thermal switch open, permanent lockout | Call a pro |
| 27.1 | Program in super plug is missing or corrupted | Call a pro |
| 27.2 | Program in super plug is missing or corrupted | Call a pro |
| 33.1 | Limit circuit switch open, blower running to cool the furnace | Safe checks first, then a pro |
| 33.2 | High heat only for the current cycle | Safe checks first, then a pro |
See all overheat codes on gas furnaces across brands.