Rheem R96VA0702317MSA Error Code 45: Low Pressure Switch Open, Inducer on High Speed

What Does Code 45 Mean?

When the Rheem R96V starts a heat cycle it energizes the induced-draft motor at high speed and then waits for the low pressure switch to close. That closure is the control's proof that the inducer is actually pulling a draft through the sealed combustion and venting system. Only after the low switch closes will the Integrated Furnace Control (IFC) allow the ignition sequence to begin. Code 45 means the inducer was commanded to high speed but the low pressure switch never closed within the allowed time, so the furnace stops before lighting.

On a 4-position condensing furnace the exhaust and intake are run in PVC to the outdoors, so anything that restricts that airflow lowers the negative pressure the inducer can develop and keeps the switch from closing. The most common cause is a blocked or improperly terminated vent: ice, snow, leaves, insect or bird nests, or a screen-covered termination outside. Vent runs that are too long or have too many elbows for the model's spec produce the same result. Inside the cabinet, a disconnected, cracked, split, or blocked pressure-switch hose, a weak or failing inducer, or a bad switch can also cause it.

Because the vent terminations are outdoors and safely reachable, a homeowner may visually check them for obvious ice, snow, debris, or nests. That is an observation only. Anything past the vent terminations, including the inducer, the pressure-switch hoses, and the switch itself, involves opening the sealed furnace and is technician-only work on this model.

Code 45 is specifically the LOW switch failing to close at HIGH inducer speed. It differs from code 46, which is the low switch open at LOW inducer speed while stepping down to low-stage heat, and from code 57, which is the HIGH pressure switch failing to close at high speed. Reading the exact code matters because each points to a different switch or inducer state.

What You'll Notice

• The furnace tries to start, the inducer spins up, but the burners never light and the display flashes 45.
• You can hear the inducer running for a while and then the furnace shuts down without heat.
• During cold, snowy, or windy weather the code appears more often, hinting at a vent restriction outside.
• The outdoor PVC vent or intake termination has visible ice, snow, leaves, or a nest partially blocking it.
• Cooling and fan-only modes still run normally even though gas heat will not start.

Common Causes

How This Is Diagnosed

The technician follows the airflow path in order. First they verify the inducer actually runs and comes up to high speed on the heat call. Next they check the outdoor intake and exhaust terminations and the full vent run for blockage, excess length, or too many elbows. Then they inspect the pressure-switch hoses for splits, kinks, condensate, or disconnection at the switch and the collector box. Finally they compare the switch's continuity against the actual draft measured at the switch port; if a strong draft is present but the switch stays open, the switch is condemned, and if the draft is weak the fault is upstream in the venting or inducer. On this two-stage model the tech confirms they are testing the low switch at high inducer speed, not the high switch or the low-speed state, before replacing any part.

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 outdoor vent terminations are clear but the furnace still shows 45 and will not light.
• The inducer runs but the burners never ignite on repeated heat calls.
• The code appears alongside a whistling or rattling pressure-switch hose inside the cabinet.
• The furnace was recently installed or re-vented and 45 started appearing, suggesting the vent run exceeds the model's limits.

✓ Verified against manufacturer service manual — March 2026