Furnace Error Codes
Furnaces communicate faults by blinking a red LED on the control board — count the blinks (for example, 3 red flashes) and match the pattern to your brand below. Many furnace lockouts clear after a power reset, but anything involving gas, burners, or the heat exchanger needs a licensed HVAC technician. Never bypass a safety switch.
Goodman furnace codes
1 (red LED) (1 red flash)
2 (red LED) (2 red flashes)
3 (red LED) (3 red flashes)
4 (red LED) (4 red flashes)
5 (red LED) (5 red flashes)
6 (red LED) (6 red flashes)
7 (red LED) (7 red flashes)
8 (red LED) (8 red flashes)
1 (amber LED) (1 amber flash)
2 (amber LED) (2 amber flashes)
3 (amber LED) (3 amber flashes)
Green LED (normal) (green LED on)
Lennox furnace codes
Common furnace problems
- How to read the code: remove the blower-door panel, find the control board, and count the red LED flashes — the pattern repeats.
- Furnace tries to start then stops: check the air filter, thermostat batteries, and that the gas valve is open.
- Pressure-switch codes: check the flue pipe outside for blockages (snow, nests, debris).
- Carbon monoxide safety: make sure you have working CO detectors — a cracked heat exchanger is dangerous and invisible.
Safety first
Work through fixes from simplest to most advanced, and stop when a guide tells you to call a technician. Never bypass safety switches, and for gas or high-voltage equipment call a licensed professional.