Coleman DGAA056BDTA Error Code 4 Flashes: Limit Switch Open

What Does Code 4 Flashes Mean?

Error code 4 Flashes on the Coleman DGAA056BDTA indicates that a primary or auxiliary limit switch has opened its normally closed contacts. The limit switch is a safety device that shuts down the burners when the air temperature around the heat exchanger climbs past a safe threshold, protecting the heat exchanger and reducing fire risk.

When this code is active, the Integrated Ignition Control keeps both the supply-air blower and the inducer running to cool the furnace down. The blower running continuously while the burners are off is the classic sign of this fault. The furnace will not resume heating until the limit switch cools and resets, which happens automatically once temperatures return to normal.

On this single-stage mobile-home furnace, overheating almost always comes down to restricted airflow across the heat exchanger, and the most common restriction is a dirty air filter. Other causes include an improperly sized duct system, an incorrect blower speed setting, an incorrect firing rate, or a failing blower motor. Because the filter is the one cause a homeowner can safely address, start there before assuming a deeper problem.

What You'll Notice

• The blower runs continuously — often for long stretches — while the burners stay off and the air feels cool
• The green LED behind the blower-door view port flashes four times, pauses about two seconds, then repeats
• The furnace heats briefly, then shuts the burners off well before the thermostat is satisfied (short cycling on high limit)
• Registers closest to the furnace feel warmer than distant rooms, a sign of weak overall airflow
• The air filter is visibly gray, matted, or clogged when you pull it out

Common Causes

How This Is Diagnosed

Diagnosis starts with airflow because that is by far the most common cause and the cheapest to correct. Check and replace the filter, then confirm every supply register and return grille is open and unobstructed, and look for crushed or disconnected ductwork. If the code returns with a clean filter and open vents, the problem lies deeper — a technician measures the furnace's temperature rise and compares it to the rating plate, verifies the blower speed setting and firing rate, and tests the blower motor and capacitor for weak performance.

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 Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). If you smell gas, leave the area immediately and call your gas company.
2. Replace the air filter Locate the air filter in the blower compartment or return air duct. Slide out the old filter and check its condition — if it is visibly dirty, gray, or clogged with dust, it is likely the cause. Install a new filter of the correct size with the airflow direction arrow pointing toward the blower.
3. Check all supply registers and return grilles Walk through every room and make sure all supply registers and return air grilles are fully open and not blocked by furniture, rugs, curtains, or other objects. Even partially closed vents reduce total system airflow.
4. Inspect accessible ductwork If you can see your ductwork in the basement, attic, or crawl space, check 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. The LED should return to steady on (normal operation).

When to Call a Professional

Contact a licensed HVAC technician if:

• The 4-flash code returns after replacing the filter and opening all vents
• The blower motor sounds labored, runs slowly, or does not spin at all
• The furnace trips the limit switch within a few minutes of starting
• You suspect the ductwork is undersized or has major restrictions
• The furnace was recently installed or had its blower speed or firing rate changed

✓ Verified against manufacturer service manual — March 2026