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Carrier gas furnace code 35.1: Modulating gas valve not communicating
Gas furnace, Canada and United States
The modulating gas valve is not communicating with the control.
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
-
The modulating gas valve stopped communicating with the control. A technician checks the valve and its wiring.
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, 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
6 models in 1 range
| Range | Models |
|---|---|
| 59MN7C | 59MN7C060C17-14, 59MN7C060C21-20, 59MN7C080C17-14, 59MN7C080C21-20, 59MN7C100C21-22, 59MN7C120C24-22 |
Where this comes from
- 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 |
|---|---|---|
| 21 | Gas heating lockout, fault in the gas valve circuit | Safe checks first, then a pro |
| 22 | Flame sensed while the gas valve is off | Safe checks first, then a pro |
| 35 | Modulating gas valve not communicating | Call a pro |
| 21.1 | 24 volts sensed at the gas valve when there should be none | Safe checks first, then a pro |
| 22.1 | Flame proved while the gas valve is off | Safe checks first, then a pro |
| 34.5 | Low heat flame lost before the blower started | Safe checks first, then a pro |
| 34.6 | Low heat flame lost after the blower started | Safe checks first, then a pro |
| 34.7 | High heat flame lost before the blower started | Safe checks first, then a pro |
| 34.8 | High heat flame lost after the blower started | Safe checks first, then a pro |
| 41.1 | No blower speed at start-up | Call a pro |
| 41.2 | Blower speed lost while running | Call a pro |
| 41.3 | Blower not reaching 500 rpm | Call a pro |
See all gas valve fault codes on gas furnaces across brands.