Ruud U96VA0702317MSA Error Code 46: Low Pressure Switch Open, Inducer on Low Speed
What Does Code 46 Mean?
A code 46 on the Ruud U96VA0702317MSA is a critical fault indicating the low pressure switch opened when the inducer was running at low speed. This fault only occurs after the furnace has successfully ignited at high fire and the IFC attempts to transition to low-stage heating by reducing inducer speed. During this transition, if the reduced inducer speed cannot maintain enough negative pressure to keep the low pressure switch closed, code 46 triggers. The gas valve is immediately de-energized, the furnace runs post-purge and blower off-delay, then attempts to restart.
The low-fire operating condition is inherently more sensitive to venting restrictions than high-fire, because the inducer runs slower and generates less negative pressure. A venting problem that is marginal at high fire may reliably fail at low fire. Common causes include partially blocked vent terminations or piping, vent run configurations near the upper limits of the installation specification, failing inducer motors that struggle to maintain speed under load, high-altitude installations where thinner air reduces inducer efficiency, and faulty pressure switches.
A technician needs to evaluate the entire venting system — pipe lengths, elbow counts, termination conditions — against the specifications for this model, as well as test the inducer motor performance and pressure switch operation.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Vent blockage or improper termination | Most common | ✗ Call a pro → |
| High altitude installation without proper kit | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Call a technician to inspect the venting system for partial blockages and verify the vent pipe lengths and elbows are within the installation manual limits for low-fire operation
- If the installation is at high elevation, the technician should determine whether a high-altitude kit is required; they should also test the inducer motor at low speed and the pressure switch under low-fire conditions
✓ Verified against manufacturer service manual — March 2026