Rheem Furnace Error 46 signifies a “Low Pressure Switch Stuck Open” fault. In technical terms, this means the Integrated Furnace Control (IFC) board has energized the inducer draft motor, but the low-pressure switch failed to close within the allotted timeframe, preventing the ignition sequence from proceeding to the gas valve stage.
⚠️ Warning: Check Manual First
For your safety and to avoid voiding the warranty, please check the official docs.
If you are encountering this error, you are likely dealing with a furnace that refuses to ignite, leaving your home increasingly cold. You might hear the inducer motor (the small fan) kick on for a brief period, followed by silence or the main blower fan running constantly as a safety “limp mode.” While a pressure switch fault can be frustrating, it is a critical safety feature designed to protect your household from improper combustion. Rest assured, with a systematic approach and basic diagnostic tools, this is an issue that can often be resolved without a full system replacement.
| Specification | Details |
|---|---|
| Difficulty Level | Intermediate (Requires electrical testing) |
| Estimated Time | 45 – 90 Minutes |
| Tools Needed | Digital Multimeter, 1/4″ Nut Driver, Phillips Head Screwdriver, Small Wire Brush or Paperclip |
| Estimated Part Cost | $0 (Cleaning) to $150 (Switch or Inducer) |
Symptoms of Error 46
When a Rheem furnace triggers Code 46, the diagnostic LED on the control board—usually visible through a small sight glass on the lower blower door—will flash four times, followed by six times, indicating the specific “Low Pressure Switch Stuck Open” status. Beyond the light code, the physical symptoms are quite distinct:
- Ignition Failure: The furnace will initiate its startup sequence, but the burners will never actually light. You will not hear the “whoosh” of gas igniting.
- Inducer Motor Cycling: The small combustion blower (inducer) will spin up for 30–60 seconds and then shut down as the board realizes the pressure switch hasn’t closed. It may attempt this several times before entering a hard lockout.
- Cold Air Circulation: In many Rheem models, the main blower fan will run continuously while the error is active. This is a safety protocol to clear any potential combustion gases, but it results in cold air blowing through your vents.
- Physical Clicking: You may hear the internal relay on the control board clicking as it tries to engage the next stage of the heating cycle, only to be stopped by the open circuit at the switch.
What Triggers this Code?
What Triggers this Code?
In a properly functioning furnace, the inducer motor creates a vacuum (negative pressure) that pulls the diaphragm inside the pressure switch closed. If the circuit stays open, the IFC assumes it is unsafe to burn gas. This failure typically stems from one of the following technical issues:
1. Venting and Flue Obstructions: This is the most common external cause. If the PVC exhaust or intake pipes are blocked by ice, bird nests, or debris, the inducer motor cannot move enough air to create the required static pressure. Because modern furnaces are highly sensitive to airflow, even a partial blockage can prevent the switch from “making” the connection.
2. Condensate Backup: High-efficiency furnaces produce water (condensate). If the furnace drain lines or the internal collector box are clogged with “gunk” or biological growth, water can back up into the pressure switch tubing. Water in the line creates erratic pressure readings or physically prevents the diaphragm from moving, resulting in an open circuit due to fluid dynamics interference.
3. Mechanical Fatigue of the Switch: The pressure switch contains a sensitive silicone diaphragm and a microswitch. Over years of thermal cycling and thousands of “on/off” operations, the diaphragm can become brittle or lose its elasticity. Additionally, internal electrical contacts can oxidize over time, increasing resistance to the point where the board no longer recognizes the switch as closed.
4. Inducer Motor Degradation: If the inducer motor’s bearings are failing or the internal impeller wheel is coated in dust and soot, the motor may spin, but not at the RPM or efficiency required to generate the specific “inches of water column” (WC) pressure needed to trip the switch. This is a subtle failure where the motor sounds “fine” to the untrained ear but is underperforming technically.
Troubleshooting & Replacement Instructions
Troubleshooting & Replacement Instructions
- Isolate Power and Gas:
Safety is paramount. Before removing any panels, switch the furnace power off at the dedicated service switch or the breaker panel. Turn the gas shut-off valve to the “off” position. This prevents accidental electrical shorts or gas leaks while you are manipulating components.
- Inspect the Pressure Switch Tubing:
Locate the small translucent or black rubber hose connecting the pressure switch to the inducer housing. Pull the hose off both ends. Inspect it for cracks, brittle spots, or moisture. If there is water inside, blow it out completely. Ensure the “port” (the small nipple the hose connects to) is not clogged with scale or debris. Use a small paperclip to gently clear the port on the inducer housing.
- Verify the Venting Path:
Check the exterior of your home where the furnace vents. Ensure that snow, ice, or vegetation is not blocking the pipes. If you suspect an internal blockage, you may need to disconnect the PVC at the furnace (temporarily) to see if the error clears. Warning: Never run the furnace for an extended period with the venting disconnected, as this will vent Carbon Monoxide into your home.
- Test with a Multimeter (Continuity Test):
Set your multimeter to the Ohms (Ω) or Continuity setting. With the power OFF and wires disconnected from the switch, place your leads on the two terminals. It should show “OL” (Open). Now, while the inducer is running (you’ll need to briefly restore power and hold the door switch), the reading should drop to nearly 0 Ohms. If the inducer is running but the switch stays at “OL,” the switch is likely defective or the inducer isn’t pulling enough vacuum.
- Check Voltage to the Switch:
Set your meter to AC Volts. With the furnace calling for heat, check for 24VAC between the switch input and the chassis ground. If you have 24V going in but nothing coming out when the inducer is at full speed, the switch is mechanically failed and requires replacement. Ensure you match the “PF” (Pressure Factor) rating on the new switch exactly.
- Examine the Condensate Trap:
If your Rheem is a 90% plus efficiency model, locate the plastic trap inside the cabinet. If it is filled with dark sediment, it may be preventing proper drainage. Remove the trap, flush it with warm water and a mild bleach solution, and reinstall it. A backed-up trap is a frequent silent killer of pressure switch circuits.
How to Prevent Error 46
To avoid a mid-winter breakdown, implement these professional maintenance standards:
- Annual Inducer Port Cleaning: During your yearly inspection, always remove the pressure switch hose and use a small drill bit (held by hand) or a wire to clear the orifice in the inducer housing. Aluminum and plastic housings often develop a small crust of oxidation that restricts air pressure to the switch.
- Install a High-Quality Filter: While the pressure switch is on the combustion side, a clogged air filter causes the furnace to run hotter and longer. This excessive heat can prematurely degrade the rubber tubing and silicone diaphragms of the pressure switch components.
- Protect the Outdoor Vent Terminations: Install a “bird screen” or a specialized concentric vent cap. This prevents rodents and birds from nesting in the pipes during the off-season, which is a leading cause of Error 46 upon the first cold snap of the year.
FAQ
Frequently Asked Questions
Q: Can I bypass or “jump” the pressure switch to get heat tonight?
A: Absolutely not. Jumping a pressure switch is extremely dangerous. The switch ensures that the exhaust gases (including Carbon Monoxide) are being properly vented. If you bypass the switch and there is a blockage, those gases will backfill into your living space. Furthermore, the IFC board performs a “pre-check” to ensure the switch is open before the inducer starts; if it sees a jumped (closed) switch at start-up, it will trigger a different error code and still refuse to light.
Q: Why does the error happen intermittently?
A: Intermittent Error 46 codes are often weather-related or moisture-related. High winds can cause pressure fluctuations in the vent pipe that “flutter” the switch. Alternatively, a partially clogged condensate drain may only back up enough to trip the switch after the furnace has been running for several hours and produced enough water to hit the “critical level” in the inducer housing.
Q: Is it okay to blow into the pressure switch to test it?
A: It is not recommended. Human lungs can easily produce over 2 PSI of pressure, whereas most Rheem furnace switches are designed to trip at less than 1.0 inch of water column (roughly 0.036 PSI). Blowing too hard into the switch can rupture the delicate internal silicone diaphragm, turning a minor cleaning job into a mandatory part replacement.