Carrier furnace Code 31 (3 short, 1 long LED blink) is a gas valve fault. The control board sends 24VAC to the valve solenoid but the valve does not open or opens incorrectly.
Code 31 is one of those frustrating ones because the furnace looks like it's working perfectly right up until the gas should flow. You'll see the ignitor glow bright orange, then absolutely nothing happens. The board's doing its job. The valve just isn't answering. Ignore it and you're stuck without heat, usually on the coldest night of the year. It's a safety lockout, which is actually a good thing.
Here's what's actually going on: the control board is sending the open command to the gas valve, but the valve's ignoring it. Before you assume the valve's toast, always check if someone bumped the manual shutoff or if there's been any recent gas work at your house that might've left air in the lines. I replaced three of these valves last month alone, so it's not an uncommon call.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Gas valve solenoid coil burned out or failed mechanically40%
Gas supply pressure too low or gas shutoff valve partially closed24%
Control board not outputting 24VAC signal to valve14%
Debris or corrosion inside valve seat blocking gas flow12%
Wiring harness to gas valve corroded or disconnected10%
Symptoms You May Notice
The inducer fan runs and the ignitor glows bright orange, but you never hear that whomp of gas igniting. The furnace just sits there with a glowing ignitor doing nothing.
3 short blinks followed by 1 long blink on the control board status LED, repeating over and over.
Furnace cycles through the full startup sequence 3 times and then goes into hard lockout, meaning no more attempts until you manually reset it.
No click from the gas valve area when the ignitor reaches full glow. That click is the solenoid firing, and if you don't hear it, the signal's not getting there or the solenoid's dead.
Your thermostat says it's calling for heat but the house is getting colder, and you can hear the furnace starting and stopping repeatedly without ever actually heating anything.
Can you reset a Carrier furnace to clear the 31 code?
Flip your thermostat to off, then cut power at the furnace power switch for a full 30 seconds. Flip it back on and wait. You'll hear the inducer motor spin up first, then the ignitor will glow. If the underlying problem's still there, Code 31 will come back within about 90 seconds. If it was just a glitch or air in the lines, it'll fire right up. Don't reset it more than 3 times in a row without diagnosing first.
Tools Required for Diagnosis
Phillips #2 screwdriverFlat head screwdriverMultimeter (VAC and ohms settings)Flashlight or headlampManometer (for gas pressure verification, licensed tech)Pipe wrench (gas line connections, licensed tech only)Leak detection spray or soapy water for post-repair gas leak check
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
ComponentComponent Under Test
Expected Range20–60 ohms
ConditionIf Open (OL) or infinite, replace component.
Replacement Parts
If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.
Part Name
OEM Number
Estimated Price
Carrier Gas Valve (Natural Gas)EF32CW194 · $85–$175
EF32CW194
$85 – $175
Frequently Asked Questions
Can I replace a Carrier gas valve myself?
Honestly, I'd really push back on this one. Replacing a gas valve isn't like swapping a fan motor. You've got to break into the gas line, which means proper pipe dope or thread tape, a solid leak test with soapy water or a detector, and ideally a manometer to verify manifold pressure afterward. Most local codes require a licensed tech for gas work, and for good reason. Get the manifold pressure wrong and you're either starving the burners or running them too rich, both of which are bad news. A small leak here can mean a house fire or CO poisoning. This one's worth paying for a pro.
What does 24VAC at the gas valve terminals mean?
Think of it as the 'go' signal from the control board. If that 24VAC shows up but the valve doesn't open, the board's healthy and the fault is in the valve itself, either the solenoid is burned out or there's a mechanical problem inside. That's actually good news in a way because it rules out a pricey board replacement and narrows it down to a single part. A Carrier-compatible gas valve runs about $80-150 in parts, versus $200-400+ for a control board. Knowing which one it is before you order parts saves you real money.
How much does it cost to fix a Carrier furnace Code 31?
Depends entirely on what's actually wrong. If it's just the manual shutoff being partially closed or air in the lines, it costs you nothing. Gas valve solenoid burned out and needs replacing? You're looking at $80-150 for the part and $150-300 in labor, so roughly $250-450 total. If the control board's relay failed and that's why there's no 24VAC signal at the valve, board replacement runs $200-400 for the part plus labor. Get the full diagnostic done before you approve any parts. Don't let anyone sell you a valve before they've proven that's actually the problem.
Why does my furnace try to start 3 times before locking out?
That's the ignition retry sequence doing exactly what it's supposed to do. Carrier builds in 3 ignition attempts before going into hard lockout because if it kept trying indefinitely, unburned gas could accumulate in the heat exchanger and that's a serious safety hazard. Three tries, then lockout. The LED blinks the code to tell you what it found. Reset the furnace, watch it try, and use that window to test for 24VAC at the valve terminals during the ignition attempt. That's your best diagnostic window.
Could a bad flame sensor cause Code 31?
No. Flame sensor issues throw different codes, usually Code 13 or Code 34 depending on your board version. Code 31 is specifically the gas valve circuit and fires before the flame sensor even gets involved in the sequence. The flame sensor only matters after gas ignites, and with Code 31, you never even get to ignition. That said, if you've got multiple codes at once, deal with them in order. But don't let someone sell you a flame sensor to fix Code 31. That's not the problem.