Coleman DGAA056BDTA Error Code 3 Flashes: Combustion Air Pressure Switch Failed to Close
What Does Code 3 Flashes Mean?
Error code 3 Flashes on the Coleman DGAA056BDTA indicates that the combustion air pressure switch failed to close at the beginning of the heat cycle. The pressure switch is a safety device that confirms the inducer motor is properly venting exhaust gases before the burners ignite. When it does not close, the furnace will not proceed to ignition.
The inducer motor starts at the beginning of each heating cycle to create a draft through the heat exchanger and vent pipe. The pressure switch senses this draft and closes its contacts to signal the control board that venting is adequate. If the switch does not close within the expected time, the control board aborts the ignition sequence and displays this fault code.
Common causes include a blocked vent pipe (ice buildup in winter, bird or insect nests, leaves, or debris), a broken or disconnected pressure switch hose, a failing inducer motor that cannot generate sufficient draft, or a faulty pressure switch. In some cases, excessive vent pipe length or too many elbows can also reduce draft below the switch's threshold.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- The vent appears clear but the 3-flash code persists
- The inducer motor sounds weak, rattles, or does not start at all
- The pressure switch hose is intact and connected but the switch still will not close
- The vent run is unusually long or has multiple elbows
- You are not comfortable working on the roof or accessing the vent termination
✓ Verified against manufacturer service manual — March 2026