Compiled & reviewed by Nikolai Tsyrenov · Updated 2026-06-25
How do I read Heil furnace error codes?
Heil furnaces display fault codes on a single diagnostic LED, where the first digit is the count of short flashes and the second digit (after a '+') is the count of long flashes.
How to read Heil furnace codes
Heil furnaces display fault codes on a single diagnostic LED, where the first digit is the count of short flashes and the second digit (after a '+') is the count of long flashes. Heil and its ICP sister brands (Tempstar, Comfortmaker, Day & Night, Arcoaire, KeepRite) use the same control. A bright-dim 'heartbeat' just means the control has power and no active fault; an LED that is on solid means the control is locked out. Read the LED through the sight glass on the blower door — stored codes are erased after about 72 hours.
The control is locked out — caused by a flame-sense circuit failure, a stuck-open gas-valve relay, or an internal software check error. It auto-resets after 1 hour; if a solid LED keeps returning after a power cycle, the control board needs service. (A bright-dim heartbeat, by contrast, is normal.)
Code 6+1 (Ignition lockout)
Ignition lockout after the control's repeated ignition attempts (code 6) all failed — gas off / low pressure, a failed igniter, a dirty flame sensor, or a grounding problem. Auto-resets after 3 hours.
Code 1+2 (Blower on after power-up)
Normal/informational, not a fault — the blower runs for about 90 seconds after power-up if the furnace was powered while calling for heat. No action needed.
⚠️ 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.
Heil furnace code FAQ
How do I read the error code on a Heil furnace?
Heil furnaces display fault codes on a single diagnostic LED, where the first digit is the count of short flashes and the second digit (after a '+') is the count of long flashes.
Where is the diagnostic light on a Heil furnace?
It's on the control board, usually visible through a small sight glass on the lower blower-compartment door. You may need to remove the door panel to read it clearly.
What is the most common Heil furnace code?
Code 2 — Pressure switch did not open — the control sensed the pressure switch was still closed when it should have been open.