Goodman Furnace Error Code 4 flashes: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Goodman furnace error code 4 flashes means: The high limit switch is open: the furnace is overheating, usually from restricted airflow. [1] Keep using it? No. Don't keep resetting it. If it locks out again, call a technician.. Start with the owner checks below, beginning with: check the air filter.

Smell gas? Leave the building now. Do not touch light switches, phones or appliances inside. Call your gas utility or 911 from outside. CO alarm sounding or headache, dizziness or nausea? Get everyone outside and call 911. Gas valves, burners, venting and wiring are for a licensed technician only. See our safety policy.

Quick facts

Code	4 flashes
Also shown as	None listed by the manufacturer
Brand / appliance	Goodman furnace (gmss96/gcss96 gas furnaces (diagnostic led flash codes))
System	Heating
Official meaning	The high limit switch is open: the furnace is overheating, usually from restricted airflow. [1]
Keep using it?	No. Don't keep resetting it. If it locks out again, call a technician.
DIY-safe?	Owner checks only (listed below)
Support	Goodman dealer or Goodman customer support (goodmanmfg.com)

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code 4 flashes means on a Goodman furnace

The high limit switch is open: the furnace is overheating, usually from restricted airflow. [1]

This is a heating code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Goodman furnace error code 4 flashes (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on Goodman's published guidance [1], rewritten for clarity.

Check the air filter. Replace or clean a dirty filter.
Open registers. Make sure supply registers and return grilles are open and unblocked by furniture or rugs.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

Air filter

When to call a technician

Licensed HVAC technician for anything inside the furnace: igniter, flame sensor, pressure switch, inducer, limits, gas valve, wiring or board
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Goodman dealer or Goodman customer support (goodmanmfg.com) first

Frequently asked questions

What does error code 4 flashes mean on a Goodman furnace?

Goodman lists 4 flashes as follows: The high limit switch is open: the furnace is overheating, usually from restricted airflow.

Is it safe to keep using the furnace with 4 flashes?

No. Don't keep resetting it. If it locks out again, call a technician..

Can I fix Goodman furnace error 4 flashes myself?

Only with the owner checks on this page, starting with: check the air filter. If it persists, call a technician or Goodman dealer or Goodman customer support (goodmanmfg.com).

Sources

https://apps.goodmanmfg.com/brochures/files/542429f6c4940SS-GMSS96.pdf (official)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Goodman.