Carrier Furnace Light Blinking? How to Read the Two-Digit Code

Carrier furnaces don't just blink — they blink in two digits, and once you know the trick, the light reads like a sentence.

Safety first, every page: smell gas anywhere? Don't reset anything. Leave the house and call your gas company from outside.

The counting trick

Watch the light through the sight glass in the lower panel. Carrier boards flash short flashes for the first digit, then long flashes for the second. So short-short-short, long = 3 and 1 = code 31. The pattern repeats; watch two or three rounds to be sure of the count.

Two rules before touching anything:

• Write down the code and your model number (sticker inside the upper compartment). Killing power erases the code.
• The real legend for your exact model is on the inside of the blower door. The codes below are common across many Carrier furnaces; the door sticker wins every disagreement.

Common Carrier codes

• 11 / steady or rapid flashing — on many models this is normal operation, not a fault. Don't panic over a calmly blinking light; check the legend.
• 13 — limit circuit lockout: it overheated repeatedly and gave up. Check the filter and open your vents, then power-cycle once.
• 31 — pressure/vent problem: the furnace can't prove its exhaust is flowing. On high-efficiency models, check the white PVC pipes outside for snow, ice, leaves, or nests. Free fix when it's a blockage.
• 33 — limit switch tripped: overheating. The classic culprit is a clogged filter or blocked return. Check the filter first, always.
• 34 — ignition proving failure: it tried to light and couldn't confirm flame. Often a dirty flame sensor; a common, modest repair.
• 14 — ignition lockout after repeated 34-type failures. Usually clears with a power cycle, then returns until the underlying cause is fixed.

What you can do before calling

Filter to the light (can't see through it, replace it). Vents open. Outside exhaust pipes clear. Then one reset: furnace power switch off 30 seconds, back on. If the same code returns, stop resetting — now you call, and you call smart, because you have the code and the model number.

Bryant owners: same board, same codes

Bryant and Carrier are the same equipment family, and most Bryant furnaces speak this exact two-digit dialect.

Related symptoms

• Furnace clicks but won't ignite
• Furnace won't turn on
• Furnace blowing cold air

Start the free troubleshooter → Free. No sign-up. It asks for the code and model — the same things a good shop asks.

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