Ruud U96VA0702317MSA Error Code 45: Low Pressure Switch Open, Inducer on High Speed
What Does Code 45 Mean?
A code 45 on the Ruud U96VA0702317MSA is a critical fault indicating the low pressure switch failed to close even though the inducer motor was running at high speed during the pre-ignition sequence. The U96VA always ignites at high fire, so this check happens every heat cycle. The switch must close after the inducer starts and before the IFC can open the gas valve for ignition — if it does not close, the ignition sequence is blocked. Cooling and fan-only modes remain available.
The most common cause is a physical obstruction in the exhaust or intake venting system. Ice and snow blocking vent terminations outside the home are frequent causes during winter. Bird nests, debris, or leaves at the vent outlets cause similar problems during other seasons. Vent pipe runs that are too long or use too many elbows — exceeding the maximum specifications in the installation manual — create airflow resistance that prevents the inducer from building sufficient negative pressure. A faulty or disconnected inducer motor, pressure switch hoses that are split, kinked, or disconnected inside the furnace, or a faulty pressure switch itself are additional causes.
As a first step, check the exterior vent pipe terminations for visible obstructions. If the vents are clear and code 45 continues, a technician must inspect the full system.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Vent blockage or improper termination | Most common | ✗ Call a pro → |
| Faulty inducer motor or disconnected pressure switch hoses | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- If exterior vents are clear and code 45 recurs, call a technician to inspect pressure switch hose connections, test the inducer motor at high speed, and verify the vent run meets the installation manual specifications
- The technician should also test the low pressure switch and replace it if it fails to close at the specified negative pressure value for this model
✓ Verified against manufacturer service manual — March 2026