Rheem Furnace Code 33: Meaning, Troubleshooting, and Repair Options

The Rheem furnace Code 33 signals a pressure switch problem that prevents safe ignition. This article explains what Code 33 means, common causes, step-by-step troubleshooting, safety precautions, likely repairs and costs, and preventive maintenance to reduce recurrences. It focuses on practical, actionable guidance for U.S. homeowners and HVAC technicians.

Item	Summary
Error Code	33 — Pressure Switch Open / Not Closing
Common Causes	Blocked vent/inducer issues, faulty pressure switch, clogged condensate/vent piping, wiring/diagnostics fault
Severity	High — furnace will not ignite until resolved; safety interlock prevents combustion
DIY Risk	Moderate to High — electrical and gas systems involved; recommended to shut off power and gas before inspection
Typical Repair Cost Range	$100–$700 depending on part replacement and labor

What Rheem Furnace Code 33 Means

Rheem furnace Code 33 indicates the system detected a pressure switch that did not close when required during the ignition sequence. The pressure switch verifies that the inducer motor and venting system are establishing the correct airflow to safely vent combustion gases. When the switch remains open, the control board prevents the igniter and gas valve from operating.

How The Pressure Switch Works

The pressure switch is a safety device that senses either positive or negative pressure created by the inducer blower. When the inducer runs, the pressure change closes the switch, signaling the control board to proceed. If the switch fails to change state, the furnace interprets it as a venting problem and locks out ignition.

Common Causes Of Code 33

• Blocked Or Restricted Venting: Animal nests, debris, snow, ice or a dislodged vent pipe can limit airflow.
• Condensate Or Debris In Pressure Tubing: Clogged rubber tubing between the pressure switch and inducer/vent can block the pressure signal.
• Failed Pressure Switch: The mechanical or internal electrical contacts can fail or the diaphragm can become worn.
• Inducer Motor Or Wheel Problems: A weak inducer that does not develop sufficient pressure will prevent the switch from closing.
• Wiring Or Connector Issues: Loose connectors, corroded terminals or broken wires can interrupt the signal.
• Control Board Or Diagnostics Fault: Less commonly, the control board may misread the switch or have a logic fault.

Symptoms Associated With Code 33

• Furnace attempts to start but locks out without ignition.
• Blower/inducer may run briefly then stop with error code displayed.
• Visible error code 33 on the furnace control panel or LED flash pattern.
• Possible unusual noises from the inducer motor or airflow obstruction sounds.

Safety First: Preparations Before Troubleshooting

Working on a gas furnace carries risk. Turn off power at the furnace switch and shut off the gas supply before inspecting components. Use insulated tools and follow manufacturer guidance. If the homeowner is unfamiliar with HVAC systems, an HVAC technician is recommended.

Step-By-Step Troubleshooting Guide

1. Confirm The Error

Check the control panel or LED flash sequence against the Rheem error code chart to ensure the displayed code is 33. Document the pattern because intermittent faults may show different codes.

2. Visual Vent Inspection

Inspect the external vent termination for obstructions like bird nests, leaves, or snow. Remove visible blockages. For sidewall or roof vents, ensure the termination cap is intact and not crushed or separated.

3. Check Inducer Operation

Restore power, set thermostat to call for heat, and observe whether the inducer motor runs smoothly. A sputtering, slow, or noisy inducer indicates a mechanical issue. If the inducer does not run, the problem may be a separate motor or capacitor fault.

4. Inspect Pressure Tubing And Connections

Locate the small rubber tubing that runs from the inducer and/or vent manifold to the pressure switch. Look for kinks, cracks, or condensate buildup. Detach tubing and blow through it gently to check for clogs. Replace if brittle or obstructed.

5. Test The Pressure Switch

With the inducer running, measure switch continuity with a multimeter or use a manometer to check vacuum/pressure. The switch should change state (open/close) as specified by the furnace. If the switch fails to actuate despite adequate inducer pressure, replace it.

6. Check Wiring And Connectors

Inspect wiring from the pressure switch to the control board. Ensure tight, corrosion-free connections. Wiggle test connectors while calling for heat to see if the error changes. Repair damaged wires with approved connectors and proper strain relief.

7. Review Condensate And Drain Lines

For high-efficiency condensing furnaces, a clogged condensate trap or drain can affect the pressure sensing path. Clear blockages and ensure the condensate discharge is flowing freely.

8. Confirm Control Board Operation

If all components test good, the issue may be the control board’s input circuit. Look for burned traces, swollen capacitors, or failed relays. Replace the control board only after verifying other causes because board replacement is costly.

When To Replace The Pressure Switch

Replacement is warranted when the switch mechanical parts fail, the diaphragm leaks, electrical contacts are unreliable, or the switch does not meet the manufacturer’s pressure rating. Use OEM or equivalent parts specified for the Rheem model and match the pressure setpoint exactly.

Typical Repair Procedures And Costs

Repair Item	Approximate Cost (Parts + Labor)
Clear External Vent Debris	$0–$150 (DIY to service call)
Replace Pressure Tubing / Clean Lines	$25–$100
Replace Pressure Switch	$75–$300
Inducer Motor Repair/Replacement	$150–$600
Control Board Replacement	$200–$700

Costs vary by region, furnace model and service provider. Labor rates and travel fees affect the final price. Ask for an itemized estimate and parts warranty before authorizing work.

DIY Tips And Tools For Homeowners

• Use a multimeter to check continuity and voltage; a manometer helps verify pressure levels.
• Avoid using adhesive tape on pressure tubing; use proper tubing clamps and replace brittle lines.
• Take photos of wire connections before disconnecting for correct reassembly.
• Do not bypass the pressure switch — that creates a dangerous condition by allowing ignition without proper venting.

When To Call A Professional

Contact an HVAC technician when gas or electrical safety is a concern, when inducer motors or control boards require replacement, or when troubleshooting steps do not resolve the code. Certified technicians carry diagnostic tools and know local codes for safe repairs.

Preventive Maintenance To Reduce Code 33 Recurrence

• Schedule annual HVAC service to inspect the inducer, pressure switch, venting and condensate systems.
• Keep outdoor vents clear of debris, snow and ice during winter months.
• Change filters regularly to maintain proper airflow and reduce stress on the system.
• Ensure condensate lines are clear and use trap treatments if recommended by the manufacturer.

Model-Specific Notes And Manufacturer Guidance

Rheem furnaces may have different pressure switch locations and part numbers by model. Always reference the furnace’s data plate, installation manual, and the Rheem technical literature for correct replacement parts and pressure ratings. Using non-specified switches can cause improper operation.

Common Misdiagnoses And Pitfalls

• Assuming the pressure switch is faulty without checking venting and inducer operation first.
• Replacing the control board prematurely; many board issues are caused by upstream component failures.
• Using generic pressure tubing that degrades faster than specified material.

Frequently Asked Questions

Can Homeowners Reset Code 33?

Simple resets can be done by turning power off for 30 seconds, then restoring power. If the underlying cause is not fixed, Code 33 will return. Resetting should be followed by inspection to prevent repeated lockouts.

Is Code 33 Dangerous?

Code 33 is a safety interlock indicating improper venting or pressure. The furnace will not ignite while the condition exists, reducing immediate combustion risk. However, any gas appliance issue should be addressed promptly to ensure safe operation.

How Long Should Troubleshooting Take?

Basic checks can take 15–45 minutes. Full diagnostics including component testing may take 1–2 hours. Replacement jobs vary—simple parts like tubing or a pressure switch are faster than inducer motor or control board replacements.

Key Takeaways

Rheem furnace Code 33 means the pressure switch did not close, preventing ignition due to a venting or airflow safety concern. Homeowners can perform visual vent checks and clear debris, but electrical, gas and component replacements should be handled by qualified technicians. Regular maintenance significantly reduces the risk of Code 33.

Resources And Links

• Rheem Official Website — Manuals, support and parts lookup.
• ASHRAE — HVAC standards and safety guidance.
• ENERGY STAR — Efficiency tips and maintenance.