Rheem Furnace Code 59: Causes, Troubleshooting, and Fixes

The Rheem Furnace Code 59 indicates a specific fault detected by Rheem control boards that points to an ignition or flame-related issue. This article explains what Code 59 means, common causes, step-by-step diagnostics, safety precautions, and when to call a professional to restore reliable heating.

Item	Quick Summary
Code Meaning	Ignition or flame sensor fault / failed trial for ignition depending on model
Common Causes	Dirty flame sensor, faulty ignitor, gas valve problem, wiring/board fault
Basic Fixes	Clean or replace flame sensor, inspect ignitor, check gas supply, reset power
When To Call A Pro	Persistent code after basic checks, gas valve/board replacement, safety concerns

What Rheem Furnace Code 59 Means

Rheem Furnace Code 59 is an error code used by Rheem and Ruud furnaces to indicate an ignition or flame detection problem. Depending on the specific control board and model, Code 59 commonly signals a flame loss or failure to establish a stable flame during the ignition sequence.

Key point: Code 59 usually relates to the ignition/flame detection system rather than general airflow or thermostat issues.

How Rheem Displays Code 59

Rheem furnaces typically show error codes via an LED on the control board or through a digital display on certain models. LED blink patterns correspond to numbers; for example, five blinks followed by nine blinks represent Code 59. Always consult the furnace manual for the exact blink pattern for the model.

Common Causes Of Code 59

Several issues commonly trigger Rheem Furnace Code 59. Identifying the root cause requires a methodical approach.

• Dirty Or Faulty Flame Sensor: Carbon buildup reduces the sensor’s ability to detect flame, causing the control board to think ignition failed.
• Weak Or Cracked Ignitor: A cracked hot surface ignitor (HSI) or a failing spark ignitor prevents reliable ignition.
• Gas Supply Problems: Closed gas valve, low gas pressure, or upstream gas line issues prevent a proper flame.
• Wiring Or Connector Issues: Loose, corroded, or broken wires between the control board, ignitor, gas valve, or flame sensor can create intermittent faults.
• Control Board Or Gas Valve Failure: Less common but possible—malfunctioning control electronics or a failing gas valve can trigger Code 59.
• Ventilation Or Draft Problems: Excessive downdraft or blocked venting can extinguish the flame after ignition.

Safety First: Precautions Before Troubleshooting

Working on a gas furnace can be hazardous. Always follow safety precautions.

• Turn off power at the furnace switch and shut off the gas supply when working on components.
• Allow the furnace to cool before touching the ignitor or burners.
• If gas odor is present, evacuate the home and contact the gas utility or emergency services.
• If unsure about any step, call a licensed HVAC technician or qualified service provider.

Tools And Materials Needed For Basic Diagnostics

Basic troubleshooting for Rheem Furnace Code 59 can be performed with common tools and replacement parts.

• Multimeter for voltage and continuity checks
• Screwdrivers and nut drivers
• Fine-grit sandpaper or emery cloth and soft brush
• Replacement flame sensor or ignitor (model-specific)
• Contact cleaner and dielectric grease for connectors

Step-By-Step Troubleshooting Guide

This approach moves from simple checks to more involved diagnostics. Perform each step carefully and note any changes in behavior or error codes.

1. Reset And Observe

Power-cycle the furnace by switching off the electrical power to the unit for 60 seconds, then restore power. If Code 59 clears and the furnace runs normally, monitor it for recurrence. Intermittent faults may reappear.

2. Inspect Error Code Pattern

Confirm the exact LED blink pattern or display code using the furnace manual. Some models use different numbering or combined error indicators.

3. Check The Flame Sensor

Remove the flame sensor and inspect it. A gray/black film indicates carbon buildup. Clean the sensor gently with fine sandpaper or emery cloth and reassemble. Tighten connections and test the furnace.

4. Test And Inspect The Ignitor

Visually inspect the hot surface ignitor for cracks. Use a multimeter to check resistance against manufacturer specs. A cracked or out-of-spec ignitor requires replacement.

5. Verify Gas Supply And Valve Operation

Confirm the gas shutoff valve is open and other gas appliances in the home function. With proper safety precautions, observe whether the gas valve on the furnace opens during the ignition attempt. If not, the gas valve or board may be at fault.

6. Check Wiring And Connectors

Inspect wiring harnesses for loose connectors, broken wires, or corrosion. Wiggle-test connections while watching the control board for changes. Use contact cleaner and ensure secure connections.

7. Measure Flame Sensor Signal And Ignitor Voltage

Using a multimeter, check flame sensor microamp signal when burners are lit per service manual. Measure ignitor voltage during the trial for ignition. These measurements often identify weak components.

8. Inspect Venting And Combustion Air

Confirm intake and exhaust pipes are clear and properly installed. Look for animal nests, debris, or severe drafts. Restricted venting can cause flame loss and trigger Code 59.

9. Swap Components Or Replace As Needed

If diagnostics point to a specific part—flame sensor, ignitor, or gas valve—replace with OEM-compatible parts. After replacement, re-test the furnace through several cycles.

When To Call A Professional

Some situations require licensed HVAC service rather than DIY repair.

• Code 59 persists after cleaning and basic checks.
• Suspected gas valve, control board, or complex electrical issues.
• Cracked heat exchanger suspected or strong gas smell present.
• Owner lacks tools, experience, or confidence to work on gas/electrical components.

Recommendation: Hire an NATE-certified or licensed HVAC technician for safe diagnosis and repair in these cases.

Estimated Repair Costs

Costs vary by model, region, and whether self-repair or professional service is used.

Repair Type	Typical Cost Range (USD)
Cleaning Flame Sensor (DIY)	$0–$20
Replacement Flame Sensor (Part)	$20–$80
Ignitor Replacement (Part + Labor)	$100–$350
Gas Valve Replacement	$300–$800+
Control Board Replacement	$200–$800+

These are general ranges; obtain written estimates from local contractors for accurate pricing.

Preventive Maintenance To Avoid Code 59

Regular maintenance reduces the risk of ignition and flame detection issues.

• Schedule annual professional furnace tune-ups before the heating season.
• Replace air filters every 1–3 months to ensure proper airflow.
• Clean flame sensors and burners periodically, especially after long summer downtime.
• Keep vents, combustion air openings, and termination points clear of debris and snow.
• Monitor for unusual odors, noises, or frequent cycling and address quickly.

Model-Specific Notes And Variations

Rheem and Ruud models may label codes differently; consult the model’s installation or service manual for precise definitions and blink patterns. High-efficiency condensing furnaces have additional sensors and pressure switches that can contribute to flame issues and may show Code 59 under different fault trees.

Frequently Asked Questions About Rheem Furnace Code 59

Can a dirty flame sensor cause Code 59?

Yes. A dirty flame sensor is one of the most common and easily fixed causes of Code 59. Cleaning often restores normal operation.

How long does it take to fix Code 59?

Simple cleaning or tightening connections can take 15–45 minutes. Replacing an ignitor or flame sensor may take 30–90 minutes. More complex repairs take longer.

Is Code 59 dangerous?

The fault itself signals safe shutdown behavior by the control board; however, underlying gas or electrical issues can be hazardous. Follow safety steps and contact a professional if unsure.

Will resetting the furnace permanently fix Code 59?

Resetting may temporarily clear the code if the condition was transient, but persistent root causes require proper diagnosis and repair.

Documentation And Resources

For accurate diagnostics, refer to the specific Rheem furnace service manual or installation guide. Manufacturer documents provide LED blink code tables, wiring diagrams, and component specifications useful for proper troubleshooting.

Key Takeaway: Rheem Furnace Code 59 commonly indicates an ignition or flame detection fault that often can be resolved by cleaning the flame sensor, inspecting the ignitor, and checking gas and wiring. If the issue persists, obtain professional HVAC service to ensure safe, lasting repair.