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 the limit switch has opened its normally closed contacts. The limit switch is a safety device that shuts down the burners when the furnace's internal temperature exceeds a safe threshold. This prevents damage to the heat exchanger and reduces fire risk.

When this code appears, the control will continue operating both the supply air blower and the inducer motor to cool down the unit. The blower running continuously without the burners firing is a clear sign of this fault. The furnace will not resume normal heating 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 across the heat exchanger. When insufficient air passes through, heat builds up until the limit switch trips. Other causes include an improperly sized duct system, incorrect blower speed setting, incorrect firing rate, or a faulty blower motor.

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 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 modified

✓ Verified against manufacturer service manual — March 2026