How to find and read your furnace's flash code
When a gas furnace runs into a problem, its control board blinks an LED in a repeating pattern. That pattern is a code, and the code table in your furnace's installation manual says exactly what it means. This guide covers finding the LED and counting the pattern correctly — then look your code up on the brand pages, where every meaning is cited to the manufacturer's manual.
Where the LED is
On most furnaces the status LED is on the control board behind the lower access door, visible through a small round window so you do not have to open anything. Look at the lower third of the furnace cabinet for a clear plastic peephole with a red, green, or amber glow. If your furnace has no window, the LED is only visible with the lower door removed — on many models removing that door also cuts power via the door switch, which resets the code, so check the window first.
Counting the pattern
- Simple counts: many brands (Goodman, Amana, York, Coleman, older Trane) flash N times, pause, and repeat. Count the flashes between pauses.
- Short + long combinations: Carrier, Bryant, and Payne boards flash a two-digit code: short flashes are the first digit, long flashes the second. Three short then three long is code 33, not six flashes.
- Two LEDs:some boards (Lennox SureLight, York red/green) use two LEDs whose combined behavior is the code — note what each one is doing.
- Displays: newer high-efficiency furnaces (Rheem/Ruud 7-segment, Lennox E-codes, Trane communicating) show the code as a number or letter code instead of flashes.
Watch through two or three full repeats before deciding what the count is. A “rapid continuous flash” and a “steady on” are also meaningful states on most brands — they are in the tables too.
The same count means different things on different brands
Four flashes is a limit-switch fault on one brand and an ignition fault on another. There is no universal table — always look the code up for your specific brand, and ideally confirm the model series listed on the code page matches yours (the rating plate inside the upper door has the model number).
Look up your brand
- Amana fault codes
- American Standard fault codes
- Bryant fault codes
- Carrier fault codes
- Coleman fault codes
- Daikin fault codes
- Fujitsu fault codes
- Goodman fault codes
- Lennox fault codes
- LG fault codes
- Mitsubishi Electric fault codes
- Payne fault codes
- Rheem fault codes
- Ruud fault codes
- Trane fault codes
- York fault codes