American Standard AUD1B080A9H31A Error Code 3 Flashes: Draft Pressure Error
What Does Code 3 Flashes Mean?
Code 3 (3 Flashes) on the American Standard AUD1B080A9H31A indicates a draft pressure error. The pressure switch is a safety device that confirms the inducer motor is creating enough airflow to safely vent combustion gases before the gas valve is allowed to open. This code appears when the pressure switch either fails to close after the inducer starts, or opens unexpectedly during the heating cycle.
There are three main areas to investigate with this code. First, a venting problem — the exhaust flue or combustion air intake pipe may be blocked by snow, ice, bird nests, or other debris. This prevents the inducer from building adequate negative pressure to close the switch. Second, the pressure switch itself may be faulty, with worn-out or stuck contacts, or a cracked diaphragm. Third, the inducer motor may be weak or failing, unable to generate sufficient draft.
Additional causes include a kinked, disconnected, or water-logged pressure switch hose, a plugged condensate drain backing up water into the inducer housing, or cracked inducer housing that leaks air. A technician can measure the actual draft pressure and compare it to the pressure switch rating to identify the root cause.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted venting (flue pipe) | Most common | ✗ Call a pro → |
| Faulty pressure switch | Common | ✗ Call a pro → |
| Inducer motor failure or weakness | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The furnace shows 3 flashes and will not ignite after verifying the exhaust vent and air intake are not blocked
- The inducer motor is running but sounds abnormally loud or weak
✓ Verified against manufacturer service manual — March 2026