Ruud U96VA0702317MSA Error Code 45: Low Pressure Switch Open, Inducer on High Speed
What Does Code 45 Mean?
Code 45 on the Ruud U96VA0702317MSA means that with the inducer energized at high speed, the low-pressure switch did not close as it should before ignition. The Integrated Furnace Control requires the switch to prove adequate draft after the inducer starts; if it stays open, the control will not allow the gas valve to open, and no heat is produced.
This is a critical fault. It is the opposite of code 44 (switch closed when the inducer is off) and the high-speed cousin of code 46, which is the same low-pressure switch failing to stay closed after the furnace drops to low-stage heating. It parallels code 57 on the high-pressure switch.
The most common cause is a blockage or improper termination in the intake or exhaust vent — check outside for ice, debris, snow, or a bird nest at the vent termination — or vent length and elbow count that exceed the maximum. A faulty or disconnected inducer, split or disconnected pressure-switch hoses, a faulty switch, or wind disrupting the draft can also cause it. Diagnosis and repair belong to a technician.
What You'll Notice
- The inducer runs but the burners never light, and the furnace shows code 45
- No heat, though cooling and fan may still work
- The problem may worsen in windy weather or when the outdoor vent is iced or blocked
- The furnace repeats the sequence without ever igniting
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 → |
How This Is Diagnosed
Because vent problems are the most common cause, a technician first inspects the intake and exhaust for blockage and proper termination, and confirms the vent length and number of elbows are within the specified maximum.
They then check the inducer motor and wiring, inspect the pressure-switch hoses for splits or disconnection, and test the pressure switch itself, replacing whichever component is at fault.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The inducer runs but the furnace never ignites and shows code 45
- You find ice, debris, or a nest at the outdoor vent termination, or suspect the vent runs are too long
- The fault persists after the vent termination has been cleared
Frequently Asked Questions
Can I clear a blocked vent that causes code 45 myself?
You can safely check the outdoor intake and exhaust terminations for obvious ice, snow, or debris, but internal vent, inducer, and pressure-switch diagnosis should be done by a technician.
Why does code 45 happen more in cold or windy weather?
Ice can form at the vent termination and strong wind gusts can disrupt draft, either of which can keep the low-pressure switch from closing at high inducer speed.
✓ Verified against manufacturer service manual — March 2026