Goodman GMEC960803BN Error Code Red 4 Flashes: Open Limit Switch

What Does Code Red 4 Flashes Mean?

Four red flashes on the Goodman GMEC960803BN's Integrated Control Module indicate an open limit circuit — the main limit, an auxiliary limit, or the rollout switch has opened. These are temperature-activated safety switches that cut the gas whenever the heat exchanger area gets too hot.

When a limit opens, the burners shut off but the multi-speed ECM blower keeps running to pull heat out of the heat exchanger. On this two-stage furnace the limit is most often tripped by restricted airflow: not enough air is moving across the heat exchanger, so heat builds up until the switch opens. The furnace will retry once temperatures fall back into range.

The most common cause is a clogged air filter. Other causes include closed or blocked supply registers, crushed or disconnected ductwork, incorrect gas pressure, misaligned burners, or a weak blower motor. This code sits at the low end of a family of overheat-related faults: if the limit and rollout stay open long enough you can escalate to red 5 flashes (rollout/fuse), and a limit that stays open for minutes with the inducer running produces red 11 flashes (blower failure).

What You'll Notice

• The furnace fires briefly, then the burners shut off while the blower keeps running
• Warm-then-cool air cycling from the registers as the furnace short-cycles on the limit
• A visibly dirty, gray, or matted air filter
• Weak airflow from the supply registers, or several registers closed or blocked
• The control board LED flashing red four times during the fault

Common Causes

How This Is Diagnosed

Diagnosis starts with airflow because that is the most common and most homeowner-checkable cause. The filter is inspected and replaced, then registers, returns, and accessible ductwork are checked for restrictions. If airflow is fine, a technician measures temperature rise across the furnace and compares it to the rating-plate range, checks gas manifold pressure and burner alignment, and finally tests each limit and rollout switch for a stuck-open condition or bad wiring.

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 power at the breaker or switch and shut off the gas supply Switch the furnace breaker OFF and turn the gas shutoff valve to OFF (handle perpendicular to the pipe). Let the furnace cool before working near it. If you smell gas, leave immediately and call your gas company.
2. Replace the air filter Find the filter in the blower compartment or return duct. If it is gray, matted, or clogged, replace it with the correct size, airflow arrow pointing toward the blower. If you recently switched to a very high-MERV filter, go back to the manufacturer-recommended rating — an over-restrictive filter can itself trip the limit.
3. Open all supply registers and return grilles Walk the house and make sure every supply register and return grille is fully open and not blocked by furniture, rugs, or curtains. Closing off too many rooms starves the furnace of return air.
4. Inspect accessible ductwork Check visible ducts in the basement, attic, or crawl space for collapsed flex duct, disconnected sections, or crushed runs that would choke airflow.
5. Restore power and gas, then test Turn the gas valve ON (handle parallel to the pipe) and the breaker back ON. Set the thermostat to call for heat and watch a full cycle to confirm the burners stay lit.

When to Call a Professional

Contact a licensed HVAC technician if:

• The code returns after replacing the filter and opening all vents
• The limit trips within a minute or two of the burners lighting
• The blower motor sounds labored, runs slowly, or does not start
• You also see red 5 flashes (rollout/open fuse) or red 11 flashes (blower failure)
• You suspect incorrect gas pressure, misaligned burners, or undersized ductwork

✓ Verified against manufacturer service manual — March 2026