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Furnace Blink Codes: Reading the Flashing Light
Most gas furnaces report faults by flashing an LED on the control board in a repeating pattern: count the flashes, note the pause, repeat. Here is the critical fact first: there is no universal blink code standard. Three flashes on a Goodman, a Carrier and a Trane can mean three different things. The chart printed on the inside of your furnace's blower door is the authority for your exact model, and it always wins over any general table, including this one.
General pattern guide (typical meanings, always confirm on your door chart)
| Code | What It Means | Guide |
|---|---|---|
| 1 blink | Often ignition failure or flame not proven: the furnace tried to light and could not confirm flame | Listed here, full guide in progress |
| 2 blinks | Often a pressure switch fault: the switch did not prove the vent is clear | Listed here, full guide in progress |
| 3 blinks | Often a pressure switch stuck open, or on some brands an ignition or limit fault | Listed here, full guide in progress |
| 4 blinks | Often a high limit switch open: the furnace overheated, classically from a dirty filter or blocked vents | Listed here, full guide in progress |
| 5 blinks | Often a flame sensor problem: flame is present but not being sensed correctly | Listed here, full guide in progress |
| 6 or more blinks, or rapid flashing | Often electrical, grounding, polarity or control board faults on many brands | Listed here, full guide in progress |
| Steady on, or slow heartbeat flash | Usually normal standby or a call for heat being handled, varies by brand | Listed here, full guide in progress |
Before You Call Anyone
Safe homeowner checks, and only these: confirm the thermostat is set to Heat and above room temperature, confirm the furnace power switch (it looks like a light switch, usually near the unit or on it) is on, check the breaker, replace a dirty air filter, and make sure supply and return vents are open and unblocked. Then count and record the blink pattern and read your door chart. Stop there. Gas valves, burners, heat exchangers, control boards and anything involving opening the gas train are professional territory, full stop. If you smell gas at any point, leave the house and call your gas utility or 911 from outside.
Frequently Asked Questions
Why do websites disagree about what 3 blinks means?
Because manufacturers assign their own meanings. Three blinks is a pressure switch fault on many Goodman furnaces and something different on several Carrier and Trane models. Your door chart is the only reliable source for your furnace.
Can I reset a furnace by turning the power off and on?
A power cycle clears a lockout on many models and is safe to try once after the simple checks (thermostat, switch, filter). A furnace that locks out again is reporting a real fault, do not keep cycling it.
How do I count a two-part blink code?
Some boards flash a first digit, pause briefly, then a second digit, then a long pause before repeating. Count both groups: for example 3 short flashes, a pause, then 1 flash is code 31 on those boards.
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