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Carrier gas furnace code 26: Burner thermal switch open
Gas furnace, Canada and United States
The burner thermal switch is open. If it opens during a call for heat, the control locks out until the power is turned off and on again.
On the status light, this code is 2 short flashes, then 6 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.
Only some models show this code. Check the list below.
What causes it
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A blocked burner inlet or burner mesh.
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Poor airflow from the inducer, or strong wind at the vent.
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On 59CU5A, a power cut while the furnace was heating, which can make the switch open.
How to read this code on your unit
The status light is on the furnace control board. On 58CU0A and 59CU5A furnaces it shows through the sight glass in the blower access door. On 58SU0A and 59SU5A furnaces it is read with the blower door off, which is a job for a technician. 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 1 long flash is code 31. 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
8 models in 2 ranges
Where this comes from
- 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 53, 65
Checked against the manufacturer's manual on 15 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 |
| 23 | Flue or venting fault (depends on model) | Call a pro |
| 24 | 24-volt fuse on the control has blown | Call a pro |
| 25 | Model plug missing or wrong, or a setup switch error | Call a pro |
| 31 | Flue or venting fault (depends on model) | Safe checks first, then a pro |
| 32 | Low or low-heat pressure switch did not close, or opened again | Safe checks first, then 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 |
| 26.1 | Burner thermal switch open, permanent lockout | Call a pro |
| 26.2 | Burner thermal switch open, permanent lockout | 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.