Goodman GMEC960803BN Error Code Red 4 Flashes: Open Limit Switch

What Does Code Red 4 Flashes Mean?

Four red flashes on the Goodman GMEC960803BN control board indicates that the limit circuit is open — either the main limit switch, auxiliary limit switch, or rollout switch has tripped. The limit switch is a safety device that shuts down the burners when the furnace overheats.

When the limit switch trips, the burners shut off but the blower continues running to cool the heat exchanger. The furnace will not fire again until the limit switch resets, which happens automatically once the temperature drops to a safe level.

The most common cause is a dirty air filter restricting airflow over the heat exchanger, causing the furnace to overheat. Other causes include restricted ductwork, closed or blocked supply registers, incorrect gas pressure, misaligned burners, or a faulty limit switch. In some cases, a failing blower motor that cannot move enough air is the culprit.

Common Causes

How to Fix It: Replace the Air Filter and Restore Airflow

What You'll Need

• Replacement air filter (matching size) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Turn off electrical power and gas supply Flip the furnace circuit breaker to OFF. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). Wait for the furnace to cool down before working near it.
2. Replace the air filter Locate the air filter in the blower compartment or return air duct. Remove the old filter and inspect it — if it is gray, matted with dust, or visibly clogged, it is likely the cause. Install a new filter of the correct size with the airflow arrow pointing toward the blower. If you recently upgraded to a high-MERV filter, consider returning to the manufacturer-recommended MERV rating.
3. Open all supply registers and return grilles Walk through every room and make sure all supply registers and return air grilles are fully open. Check that furniture, rugs, curtains, or stored items are not blocking any vents.
4. Inspect accessible ductwork Check visible ductwork in the basement, attic, or crawl space for collapsed flex duct, disconnected sections, or crushed portions that would restrict airflow.
5. Restore power and gas, then test Turn the gas supply valve to ON (handle parallel to the pipe) and flip the circuit breaker to ON. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• The code returns after replacing the filter and opening all vents
• The blower motor sounds labored or runs at low speed
• The limit switch trips within minutes of the furnace starting
• You suspect the ductwork is undersized or has significant restrictions
• You also see red 5 flashes (rollout/fuse detect)

✓ Verified against manufacturer service manual — March 2026