The short answer
Codes 21 and 22 on a Carrier furnace in Northern Virginia are gas valve faults, and they’re codes to call about, not tinker with. 21 is a gas heating lockout: the board saw power on the gas valve circuit when it shouldn’t have, and it won’t reset itself. 22 means the board sees a flame while the gas valve is supposed to be off, which points at a valve that’s stuck open or leaking through. 23 is the odd one out: the pressure switch stayed closed when it should have been open.
The three codes at a glance
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| Code | Flashes | What it means | What to do |
|---|---|---|---|
| 21 | 2 short, 1 long | Gas heating lockout: power sensed on the gas valve circuit when it shouldn’t be | Power off 5 minutes, back on once; if 21 returns, call |
| 22 | 2 short, 2 long | Flame sensed with the gas valve off | Gas off at the furnace, power off, call |
| 23 | 2 short, 3 long | Pressure switch didn’t open | Call; usually the switch’s tube or the switch |
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Code 22: a flame that shouldn’t be there
When the board sees a flame with the gas valve turned off, Carrier’s control runs the inducer motor until the flame clears, to keep pulling exhaust out the vent. Carrier’s checklist for it is short: a gas valve that’s stuck open or leaking. You’ll hear the inducer running when the furnace isn’t heating, and you may see a flame through the burner window with the thermostat satisfied.
Turn the gas off at the shutoff on the pipe going into the furnace (handle across the pipe is off), turn the furnace power switch off, and call. If you smell gas, don’t flip any switches: leave the house and call your gas company or 911 from outside.
Code 21: a gas valve circuit lockout
21 means the board found power on the gas valve circuit at a moment it shouldn’t be there. Carrier’s list of causes: the gas valve relay on the control board, miswiring, or a short in the gas valve wire. Carrier’s step is to turn the power off for 5 minutes and back on. If 21 comes back, the board or the wiring needs a technician with a meter, and it’s not a part to guess at.
Code 23: the pressure switch stayed closed
Before it lights, the furnace checks that the pressure switch is open while the inducer is still off. If the switch already reads closed, the board flashes 23 and won’t start. Carrier’s checklist: a blocked pressure tube or a switch stuck closed. It’s the mirror image of code 31, where the switch won’t close.
How to read the code
Look through the small window in the lower door. Short flashes are the first digit and long flashes are the second, so 22 is 2 short and 2 long, then a pause before it repeats. A steady light is normal, and rapid flashing means the line voltage polarity is reversed. On older boards with a red light, cutting the power erases the code, so count it before you flip the switch. Newer Carrier boards keep the last 7 faults through a power cut and print a code with a third digit, like 14.1, on a small display. Our full list of Carrier furnace codes has every one.
What not to do
Don’t keep resetting a 22 to get heat back. A furnace that sees flame with the valve off is not one to run. Never jump or bypass a safety switch to get heat back. Each one is there to stop the furnace from burning gas when something is wrong, and the wrong thing is often exhaust, which carries carbon monoxide. If your carbon monoxide alarm sounds, get everyone outside and read our CO alarm guide from there.
What a technician does
For 21 and 22 we test the gas valve and the board’s valve relay with a meter, check the wiring from the board to the valve, and watch a full cycle with a gauge on the valve. For 23 we check the tube and the switch. Gas valve and board repairs get priced before we start.
What it costs to have us look
A repair visit starts with a flat $99 diagnostic, and you get the price of the fix before we touch anything. Our Carrier repair page lists what the common repairs cost. Our heating check is $67 per system, through December 31: furnace, heat pump or boiler.
Related: furnace won’t turn on, furnace burning smell, the full Carrier code list and our Carrier repair page.
Every code meaning here comes from Carrier’s own documents: 58SC0A installation instructions and 59MN7C manual.
Call or book
Call (703) 997-9757 and tell us the code you counted, or book online from goswiftpro.com/cookiesoffer and a box of warm cookies comes with the visit. Rated 5.0 stars across 1,138 reviews on Google, Angi, Yelp, the BBB and Facebook, Virginia Class A license 2705192276.
Questions people ask
What does code 22 mean on a Carrier furnace?
The board sees a flame while the gas valve is supposed to be off. Carrier points at a gas valve that’s stuck open or leaking through.
Is Carrier code 22 dangerous?
It can be. Turn the gas off at the furnace’s shutoff, turn the power off and call. If you smell gas, leave the house and call your gas company or 911 from outside.
How do I clear code 21 on a Carrier furnace?
Carrier says turn the power off for 5 minutes and back on. If 21 comes back, the gas valve circuit needs a technician.
What does code 23 mean on a Carrier furnace?
The pressure switch didn’t open when it should have. Carrier points at a blocked pressure tube or a switch stuck closed.
