Updated 2026-06-25

Furnace Flash Codes, Decoded by Brand

Your furnace is blinking a code at you. Look up exactly what it means — and which checks are safe to try yourself — by brand.

9 brands
Animated flash-code demos
Sourced from manufacturer manuals

Furnace flash-code finder

Pick your brand, then tap the code (or the number of times your light flashes) for an instant answer.

Your furnace brand

Or browse furnace codes by brand

Carrier furnace codes11 codes Goodman furnace codes11 codes Trane furnace codes12 codes Lennox furnace codes10 codes Rheem furnace codes10 codes York furnace codes12 codes Heil furnace codes11 codes Frigidaire furnace codes10 codes Armstrong Air furnace codes12 codes

All brands → · How to read a flash code →

⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.