York TM9V080B12MP11 Error Code 3 Red Flashes: Pressure Switch Open
What Does Code 3 Red Flashes Mean?
The 3 red flashes code on the York TM9V080B12MP11 indicates the pressure switch contacts are open when they should be closed. The furnace cannot verify that exhaust gases are being safely vented, so it will not ignite until this issue is resolved.
The pressure switch is a safety device connected to the inducer 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 airflow. If the switch does not close, the control board will not allow the ignition sequence to proceed.
The manual lists several possible causes: a blocked vent pipe, a broken or disconnected pressure switch hose, disconnected wiring, a faulty inducer motor, or a faulty pressure switch. A blocked exhaust vent is the most common and most easily addressed cause.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- The vent pipes appear clear but the 3 red flashes 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