Trane TUD1B080A9H31B Error Code 3 Flashes: Draft Pressure Error
What Does Code 3 Flashes Mean?
The 3-flash code on the Trane TUD1B080A9H31B indicates a draft pressure error. The furnace cannot confirm that exhaust gases are being safely vented outside your home, so it will not ignite until this issue is resolved.
The pressure switch is a safety device connected to the inducer (draft) motor housing by a small rubber hose. When the inducer motor runs, it creates negative pressure that pulls the pressure switch closed, confirming proper venting. If the switch does not close, the control board will not allow the gas valve to open.
The manual lists three possible causes: a venting problem (blocked exhaust pipe), a pressure switch malfunction, or an inducer motor failure. A blocked exhaust vent is by far the most common cause, especially during winter when snow and ice can obstruct the vent termination outside your home.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted vent pipe | Most common | ✗ Call a pro → |
| Faulty pressure switch | Common | ✗ Call a pro → |
| Failed inducer motor | Uncommon | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The vent pipes appear clear but the 3-flash code persists
- The inducer motor sounds unusually loud, rattles, or does not start at all
- You notice the pressure switch hose is cracked, disconnected, or has water in it
- The code returns intermittently, especially on windy days
✓ Verified against manufacturer service manual — March 2026