Goodman Furnace 4 Flashes: Limit Circuit Open, Furnace Overheating (Meaning, Causes, Fixes)

What the code means

Goodman's troubleshooting charts list 4 flashes as "primary or auxiliary limit circuit is open." The limit is a safety switch near the heat exchanger that opens when the furnace runs too hot. When the control sees the limit open, it shuts off the gas and runs the circulator blower (and on many models the inducer) to cool the heat exchanger, so the symptom is a blower that runs continuously with no heat. The primary limit resets itself automatically once it cools. On Goodman 90% furnaces, if the limit opens five times in a single call for heat, the control locks out for one hour while still showing 4 flashes; cycling 115-volt power resets it. On those boards, a limit that stays open longer than 5 minutes changes to an 11-flash code (blower assumed failed), and one still open after 15 minutes changes to 5 flashes (rollout switch or fuse assumed open). Newer Goodman boards with a character display show this fault as EE3 (open high limit switch) instead of flashes.

Likely causes

• A dirty or clogged air filter, which starves the heat exchanger of airflow (Goodman lists blocked filters first)
• Blocked or restrictive ductwork, including closed or furniture-covered supply registers and blocked return grilles
• A circulator blower set to too low a speed for heating, or a weak or failed blower motor or capacitor
• A dirty blower wheel or a dirty evaporator (AC) coil above the furnace restricting airflow
• A faulty primary or auxiliary limit switch that opens too early or won't close
• Loose or improperly connected wiring in the limit circuit
• Over-firing from gas pressure set too high (a technician checks this against the rating plate)

Safe DIY checks

1. Count carefully through the sight window on the blower door: 4 short flashes and a pause is this code. Write it down before cutting power, because Goodman notes the flash code stops when power is interrupted.
2. Check the air filter first. If it's gray, matted or you can't see light through it, replace it with the same size printed on the filter frame.
3. Walk the house and open every supply register, and make sure return air grilles aren't blocked by furniture, rugs or curtains.
4. Make sure the blower door is fully closed and latched, since the door switch cuts power to the furnace.
5. Reset by turning the furnace off at its power switch or breaker for at least 30 seconds, then back on, and set the thermostat to call for heat. A lockout on 90% models clears when 115V power is cycled.
6. Watch a full heating cycle. If the burners light, run a few minutes, shut off and the blower keeps running with 4 flashes again, airflow or the limit is still the problem and it's time to call a pro.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 3 flashes Goodman Gas Furnace 3 flashes
• 6 flashes Goodman Gas Furnace 6 flashes
• 24 Carrier Gas Furnace 24
• 33 Carrier Gas Furnace 33
• CL Carrier Gas Furnace CL
• C2 Lennox Gas Furnace C2

All Goodman codes →

Sources

1. Goodman GKS9 installation manual, troubleshooting chart (4 flashes: primary or auxiliary limit circuit open; causes and corrective actions)
2. Goodman gas-fired warm air furnace manual, troubleshooting chart (4 flashes: circulator blower runs continuously; LED code ceases when power is interrupted)
3. Goodman GMEC96 service manual, limit fault codes (4 flashes, five-trip one-hour lockout, 11- and 5-flash escalation)
4. Goodman Service and Troubleshooting RS6612020, checking the primary limit control (automatic reset bi-metal limit)
5. High Ground Service Pros, Goodman error code table transcribed from Goodman manual RS6621301 (EE3: open high limit switch)