Carrier Furnace Code 35: Gas Valve Fault (Modulating Furnaces)
What the code means
Carrier status codes are two digits: the first digit is the number of short flashes and the second the number of long flashes, so code 35 is 3 short flashes followed by 5 long flashes. Code 35 appears on Carrier's modulating furnaces, which use an electronic gas valve with a stepper motor instead of a simple on/off valve. Carrier's 59MN7A Series 100 troubleshooting guide defines it as GAS VALVE FAULT: the modulating gas valve failed to respond to a command from the furnace control, or power to the gas valve electronics was interrupted. On every cycle, after the medium pressure switch closes, the control sends the valve a 1-second PWM (pulse width modulation) command, and the valve answers with the command it received; if the answer doesn't match, the control resends it up to 5 more times. The valve then moves its stepper motor and sends a PWM-DONE message. If the valve doesn't answer with the command or with PWM-DONE, the control flashes 35, shuts the unit down, waits 2 minutes, stops flashing 35 and restarts the heating cycle. The same exchange happens whenever the blower turns on or the gas rate changes, so the code can also show up when the blower starts. Code 35 can also flash at the end of the furnace's component test, where Carrier lists it as one of the possible results (11, 25, 35, 41 or 42). Because the messages are only 1-second bursts, Carrier says the valve is hard to troubleshoot and uses the component test to send it a test command.
Likely causes
- An intermittent or loose RED, YELLOW or ORANGE wire at the gas valve or at the PL8 connector on the furnace control (the check Carrier's service label lists)
- An open wire or bad terminal in the main wire harness between the control's PL8 connector and the gas valve's PL17 connector
- No 24 volts reaching the gas valve's electronics, or 24-volt power to the stepper motor electronics that cuts in and out
- A failed modulating gas valve (Carrier's guide replaces the valve when it doesn't put out its 4-volt or 5-volt signals or doesn't respond during the component test)
- A failed modulating furnace control that isn't sending 24 volts or the PWM command to the valve
- Electrical interference from an accessory such as a humidifier or electronic air cleaner, or from the blower motor, when the code flashes as the blower turns on
Safe DIY checks
Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.
- Confirm the code: look through the sight glass on the blower door and count 3 short flashes followed by 5 long flashes. Write it down before turning power off.
- Watch what the furnace does next. After a code 35 the control waits 2 minutes and restarts the heating cycle on its own, so one occasional code isn't an emergency, but a code that keeps coming back needs a technician.
- Note when it happens: at the start of a cycle before the igniter glows, when the blower turns on, or at random. Carrier's troubleshooting branches on exactly that, so it saves the technician time.
- If you have a humidifier or electronic air cleaner wired to the furnace and the code shows up when the blower starts, mention it. Carrier's guide checks whether an accessory is creating electrical interference with the gas valve.
- Make sure the gas valve's manual ON/OFF switch and the manual shut-off valve on the gas pipe are on, and that the blower door is seated so the door switch is closed.
- If you smell gas at any point, don't try to relight or reset anything: leave the house and call your gas utility or 911 from outside.
🛠 When to call a pro
- The code repeats on more than an occasional cycle, or the house isn't getting heat.
- Checking for 24 VAC across the RED and GREEN/YELLOW wires at the gas valve, and across PL8-1 and COM-24V on the control; if the control has it but the valve doesn't, the harness is repaired or replaced, and if the control doesn't, Carrier replaces the control.
- Checking for about 4 VDC across the YELLOW and GREEN/YELLOW wires at PL17 and about 5 VDC across the ORANGE and GREEN/YELLOW wires, then watching those voltages dip briefly during the component test (setup switch SW1-6) to confirm the valve and control are talking.
- Checking continuity of the YELLOW and ORANGE wires between PL8 and PL17, and both ends of the RED wire if the code flashes when the blower turns on. Carrier warns that jamming a meter probe into PL8 can damage its terminals.
- Disconnecting accessories to rule out electrical interference; if the code still appears when the blower starts, Carrier's guide replaces the gas valve and, if the problem continues, the entire blower motor including its control module.
- Never jumper or bypass a safety device, and leave gas valve replacement and gas pressure work to a qualified technician.
Parts that commonly fix it
Always match the part number to your exact model.
Modulating gas valve (exact OEM part for your model)
Modulating valves are model-specific and have a propane conversion jumper; a technician should match and install it.
Search eBay →Furnace wire harness or control board (exact OEM part for your model)
Replace only after the voltage and continuity checks point to it.
Search eBay →Digital multimeter
For checking 24 VAC and the 4 to 5 VDC signal wires at the gas valve.
Search eBay →Gas leak detector
For a quick check around the valve and gas fittings after any service.
Search eBay →Sources
Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.