Ruud U802VA050317MSA Error Code T045_F: Inducer Lo Pressure Switch Won't Close (Transient)
What Does Code T045_F Mean?
Code T045_F on the Ruud U802VA indicates that the low-stage inducer pressure switch failed to close within 60 seconds after the inducer motor started. The pressure switch is a safety device that verifies proper exhaust draft before allowing ignition. If it cannot confirm draft, the furnace enters a 5-minute lockout before retrying. The 'T' prefix means this is a transient (intermittent) fault.
During a normal startup sequence, the inducer motor (draft fan) spins up first to create a negative pressure in the heat exchanger and vent system. The pressure switch detects this negative pressure and closes, signaling the control board that it is safe to proceed with ignition. If the switch does not close, the furnace will not light.
The most common cause is a blocked or partially obstructed exhaust vent. Ice buildup, snow, bird nests, leaves, or other debris at the vent termination outside your home can restrict the draft enough that the pressure switch cannot close. A cracked or disconnected pressure switch hose or a failing inducer motor are less common but possible causes.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked vent or flue pipe | Most common | ✓ DIY fix → |
| Weak or failing inducer motor | Common | ✗ Call a pro → |
| Cracked or disconnected pressure switch hose | Common | ✗ Call a pro → |
How to Fix It: Clear the Exhaust Vent Blockage
What You'll Need
Steps
- Turn off electrical power at the breaker or power switch AND shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF, or use the power switch on or near the furnace. Turn the gas shutoff valve to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company.
- Locate the exhaust vent termination outside Find where the furnace exhaust vent exits your home. On a high-efficiency furnace like the Ruud U802VA, this is typically a PVC pipe that exits through a side wall. Check for ice, snow, bird nests, leaves, insect nests, or any other debris blocking the opening.
- Clear any visible blockage from the vent If you find ice buildup, carefully break it away from the vent opening. Remove any debris, nests, or obstructions. Make sure both the exhaust vent and the intake air pipe (if separate) are clear. Do not push debris further into the pipe.
- Check the intake air pipe as well If your furnace has a separate combustion air intake pipe (usually a second PVC pipe near the exhaust), check that it is also clear. A blocked intake pipe can also prevent proper draft and cause pressure switch failures.
- Restore gas and power, then test Turn the gas supply valve to ON and restore electrical power. Set the thermostat to call for heat. Listen for the inducer motor to start, followed by the click of the pressure switch closing, and then ignition. The furnace may need to wait out the 5-minute lockout or you can cycle the power to reset.
When to Call a Professional
Contact a licensed HVAC technician if:
- The exhaust vent is clear but the pressure switch still will not close
- You hear the inducer motor running but it sounds weak or strained
- The pressure switch hose is visibly cracked, disconnected, or has water in it
- Code T045_F keeps recurring after clearing the vent
- The inducer motor does not start at all when the furnace calls for heat
Sources
✓ Verified against manufacturer service manual — March 2026