Ruud Furnace Code 59: Meaning, Diagnosis, and Repair Steps

The Ruud furnace error “Code 59” signals an issue with the unit’s pressure switch circuit. This article explains what Code 59 means, common causes, step-by-step troubleshooting, safety precautions, and when to call a professional. The goal is to give homeowners clear, actionable guidance while highlighting key checks technicians typically perform.

Item	Summary
Error	Ruud Furnace Code 59
Primary Cause	Pressure switch circuit fault or blocked vent/ inducer problem
Common Fixes	Check venting, inspect pressure tubing, test pressure switch and inducer motor, replace faulty components
Skill Level	Basic checks for homeowners; electrical/gas and component replacement requires licensed technician

What Is Ruud Furnace Code 59?

Ruud Furnace Code 59 is an error code indicating a problem related to the furnace’s pressure switch or its circuit. The pressure switch ensures the inducer motor creates the correct draft before ignition. If the control board does not receive the expected signal from the switch, the unit will lock out and display Code 59 to prevent unsafe operation.

How The Pressure Switch Works

The pressure switch monitors negative or positive pressure created by the inducer blower to confirm proper venting. When the inducer runs, the switch closes and sends a confirmation signal to the control board. If the switch does not close or the board does not detect closure, the furnace won’t proceed to ignition.

Common Causes Of Code 59

Several issues can trigger Code 59. Identifying the correct cause guides an effective repair.

• Blocked Venting Or Chimney: Obstructions, snow, nests, or closed dampers can restrict airflow and prevent the pressure switch from seeing proper draft.
• Faulty Pressure Switch: A failed switch can remain open or short internally and fail to signal the control board.
• Damaged Or Disconnected Tubing: The small vacuum tubing between the inducer housing and pressure switch can be cracked, pinched, or disconnected.
• Inducer Motor Failure: If the inducer does not produce sufficient draft due to motor faults or bearings, the pressure switch will not close.
• Blocked Condensate Drain (High-Efficiency Units): Condensate buildup can restrict pressure sensing paths on condensing furnaces, impacting switch operation.
• Control Board Or Wiring Issues: Loose connectors, broken wires, or a faulty control board can prevent detection of the switch closure.

Safety Precautions Before Troubleshooting

Working on gas or electrical components carries risk. Follow these safety steps before performing any checks.

• Turn Off Power: Switch off power to the furnace at the breaker and use the service switch if available.
• Turn Off Gas: For any work involving ignition components, shut off the gas supply to the furnace.
• Use Proper Tools: Use insulated tools for electrical checks and a multimeter rated for household use.
• Know When To Call A Pro: If the diagnosis or repair requires gas valve work, control board replacement, or complex disassembly, engage a licensed HVAC technician.

Step-By-Step Troubleshooting Guide

1. Observe The Furnace Behavior

Note the furnace LED pattern and whether Code 59 is steady or intermittent. Document when the error appears—immediately on start, after inducer runs, or randomly—this helps narrow causes.

2. Check Venting And Outdoor Exhaust

Inspect exterior vent caps for obstructions like snow, leaves, or bird nests. For power-vent or direct-vent systems, ensure there is no restriction and that the termination point is clear and properly sloped.

3. Inspect The Inducer Motor

Restore power temporarily to observe the inducer. The inducer should start and reach speed quickly. If it hums, runs slowly, or fails to start, the motor, capacitor (if present), or wiring might be faulty.

4. Examine Pressure Tubing

Locate the small rubber or plastic tube between the inducer housing and the pressure switch. Check for cracks, oil/soot contamination, kinks, or disconnection. Replace brittle or damaged tubing.

5. Test The Pressure Switch Electrically

With power on and inducer running, measure across the switch terminals with a multimeter set to continuity or DC volts. The switch should close (continuity) when the inducer creates proper draft. If it doesn’t close, the switch may be bad or the inducer insufficient.

6. Inspect Wiring And Connectors

Check connectors at the pressure switch and control board for corrosion or loose pins. Wiggle-test wires with power off and use a multimeter to test continuity from switch to board.

7. Check Condensate Or Drain Blockage (Condensing Furnaces)

For high-efficiency condensing models, verify the condensate trap and drain are clear. A blocked drain can flood pressure sensing ports or restrict flow, causing false Code 59 triggers.

8. Test Or Replace The Pressure Switch

If tubing, inducer, and wiring are good but the switch fails to close, the pressure switch should be replaced. Replace with the manufacturer-specified part to ensure correct pressure rating and polarity.

Diagnostic Tools And Tests

Using the right tools speeds diagnosis and ensures safety.

• Multimeter: For measuring continuity, voltage, and resistance at the switch and control board.
• Manometer (Optional): Measures inducer negative pressure to verify the switch operates at the correct vacuum rating.
• Hand Vacuum Pump: Applies vacuum to pressure switch to test closure without running the inducer.
• Basic Hand Tools: Screwdrivers, pliers, and replacement tubing and connectors.

How Technicians Approach Code 59

HVAC professionals follow a systematic workflow: verify symptoms, inspect venting, test inducer and switch voltages, check control board inputs, and replace defective parts. They document measurements and may run extended diagnostics to confirm a repair.

Common Repair Costs And Time Estimates

Repair costs vary by cause. Homeowner-level checks (clearing vents, replacing tubing) are low-cost and quick. Professional repairs may be needed for motors, switches, or control boards.

Repair Item	Typical Cost Range (US)	Estimated Time
Clear Vent/Cap	$0–$100	15–60 minutes
Replace Pressure Tubing	$10–$40	15–30 minutes
Replace Pressure Switch	$75–$200	30–90 minutes
Replace Inducer Motor	$200–$600	1–3 hours
Control Board Diagnosis/Replacement	$150–$800	1–3 hours

When To Call A Licensed HVAC Technician

Call a pro if the problem involves gas valve work, complex electrical diagnostics, inducer motor replacement, persistent error codes after basic checks, or if the homeowner is uncomfortable with safety risks. Licensed technicians carry the tools and training to safely handle gas and control systems.

Preventive Maintenance To Avoid Code 59

Regular maintenance reduces the chance of Code 59. Recommended preventive actions include annual furnace tune-ups, visual vent inspections, filter replacement every 1–3 months, and keeping outdoor vent terminations clear.

• Annual Service: Professional inspection and cleaning of inducer, burners, and heat exchanger.
• Filter Management: Replace filters on schedule to reduce airflow restrictions and help the unit operate efficiently.
• Vent Clearance: Seasonal checks of outdoor vents for debris or nesting animals.

Frequently Asked Questions About Code 59

Can a dirty filter cause Code 59?

While a dirty filter primarily affects airflow and heat exchange, severe restriction can alter combustion draft and indirectly contribute to pressure switch issues, but it is not the most common cause.

Is Code 59 dangerous?

Code 59 itself is not dangerous; it is a protective lockout preventing ignition when pressure sensing is abnormal. The code helps avoid unsafe combustion conditions. However, unresolved issues affecting venting should be addressed promptly.

Will resetting the furnace clear Code 59?

Resetting may temporarily clear the code, but if the underlying cause persists the error will return. Resetting should only be used as a diagnostic step after safety checks.

Key Takeaways

Ruud Furnace Code 59 points to a pressure switch or inducer/venting problem. Homeowners can perform visual vent checks, inspect tubing, and observe the inducer. Electrical testing and component replacement should be handled by qualified technicians. Regular maintenance reduces the risk of recurrence.

For persistent Code 59 errors or any uncertainty during troubleshooting, contacting a licensed HVAC technician ensures safe, correct diagnosis and repair.