The short answer
Code 34 on a Carrier furnace in Northern Virginia means the burners were supposed to light but the control board never proved a flame. After 4 tries it locks out and flashes 14, which clears after 3 hours or a power cut. Carrier’s checklist runs in order: gas on, igniter glowing, gas valve opening, burners lighting, and then the flame sensor, a thin metal rod that a light coating can blind.
What you’ll notice
Which of these you see points at the cause:
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Swipe to see all columns →
| What happens | What it points at |
|---|---|
| The igniter glows, the burners light for a few seconds and go out | The flame sensor, or its wire and ground |
| The igniter glows, but no flame ever shows | Gas supply, gas pressure or the gas valve |
| Nothing glows at all | The igniter or the power to it |
| It lights fine sometimes and fails other times | A weak flame signal or a gas pressure problem |
The light flashes 3 short and 4 long for 34, then 1 short and 4 long once it locks out.
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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 34 is 3 short and 4 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 34.5, on a small display. Our full list of Carrier furnace codes has every one.
On newer boards the third digit narrows it down. 34.5 and 34.6 mean the flame dropped before the blower came on, and 34.7 and 34.8 mean it dropped after. A 14.1 is 4 failed tries, 14.2 is the flame lost 3 times after running 70 seconds, and 14.3 is 7 flame losses in one call for heat.
Carrier’s checklist, in order
- The gas valve switch is on and the manual shutoff on the gas line is open.
- The furnace ground wire is connected.
- The igniter glows within its 15 second warm-up, and 115 volts reaches it.
- 24 volts reaches the gas valve, and the valve opens.
- The burners light and carry flame across.
- The flame sensor: cleaned with fine steel wool, then the signal read in microamps. Carrier’s normal range is 4.0 to 6.0.
- If the sensor reads low after cleaning, the electrode, then the control board.
What you can safely check
- Find the gas shutoff on the pipe going into the furnace. The handle should line up with the pipe. If someone just did gas work in the house, this is the first place to look.
- See whether your other gas appliances work, like the stove or water heater. If none do, call the gas company.
- Count the code, then turn the furnace switch off for 30 seconds and back on, once.
- If you’re handy, our flame sensor guide shows the cleaning. Power off first, and go easy: the igniter sits right next to it and cracks if you bump it.
What not to do
Don’t keep cycling the power over and over to force it to light. Each try sends gas to the burners, and a furnace that won’t prove its flame is telling you something. If you smell gas, don’t flip any switches: leave the house and call your gas company or 911 from outside.
What a technician does
We watch a full ignition sequence, read the flame signal in microamps, check the igniter and the gas pressure at the valve, and look at the ground and the sensor wire. Most of the time the fix is on that list, and you hear the price before we do it.
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 flame sensor problems, furnace won’t turn on, furnace short cycling and the full Carrier code list.
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 34 mean on a Carrier furnace?
The burners were supposed to light, but the control board never proved a flame. After 4 tries it becomes code 14, an ignition lockout.
Is Carrier code 34 always the flame sensor?
No. Carrier’s checklist starts with the gas supply and the igniter, then the gas valve, then the flame sensor. A dirty sensor fits the furnace that lights for a few seconds and goes out.
Why is my Carrier furnace flashing code 14?
14 is the ignition lockout: 4 tries with no proven flame. It clears after 3 hours or a power cut and tries again. If it locks out a second time, call.
Can I clean a Carrier flame sensor myself?
Carrier’s fix is fine steel wool on the rod with the power off. Be gentle, because the igniter sits next to it and cracks easily.
