American Standard AUH1B080A9H31A Error Code 3 Flashes: Pressure Switch Error
What Does Code 3 Flashes Mean?
Code 3 (3 Flashes) on the American Standard AUH1B080A9H31A indicates a pressure switch error. The pressure switch is a safety component that confirms the inducer motor is pulling adequate draft through the heat exchanger and exhaust system before allowing gas to flow. When the switch fails to close or reopens during a heating cycle, the IFC board shuts down the ignition sequence to prevent unsafe venting of combustion gases.
Blocked venting is the most frequent cause. Check outside where the exhaust and intake pipes exit the building — snow, ice, leaves, bird nests, or insect nests can restrict airflow. For this condensing furnace model, also check the condensate drain for blockages, as a backed-up drain can flood the inducer housing and prevent proper operation.
If the venting appears clear, the issue may be with the pressure switch itself (worn diaphragm, stuck contacts), the pressure switch hose (kinked, disconnected, or containing water), or the inducer motor (failing, running too slowly). A technician can use a manometer to measure the actual draft pressure and compare it to the pressure switch rating to pinpoint the problem.
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 after confirming the exhaust vent and air intake are clear of obstructions
- The inducer motor sounds unusually loud, quiet, or runs erratically
✓ Verified against manufacturer service manual — March 2026