Rheem furnaces, widely used in American homes, use error codes to signal safety shutdowns and system faults. Code 59 is one such fault that warrants careful diagnosis. Because Rheem models vary, the exact meaning of Code 59 can differ between gas furnaces and multi‑stage systems. This guide explains common interpretations, typical causes, and practical steps to diagnose and address Code 59, plus when to call a professional. Readers will find actionable troubleshooting tips, safety reminders, and maintenance practices to reduce the odds of this code returning.

What Error Code 59 Indicates On Rheem Furnaces

In Rheem gas furnaces, error code 59 generally triggers a control lockout or an ignition fault that prevents the furnace from starting after one or more failed attempts. The specific definition depends on the control board and model. Some Rheem units reserve Code 59 for flame sensor or ignition system faults, while others map it to a safety switch or venting issue. To confirm the precise meaning for a particular unit, consult the owner’s manual or contact Rheem support with the model and serial numbers.

Common Causes Of Code 59

Ignition system failure, including a faulty hot‑surface igniter (HSI) or intermittent ignition transformer
Dirty or faulty flame sensor that prevents a stable flame from being detected
Inadequate gas supply or a malfunctioning gas valve or gas pressure regulator
Venting issues such as a blocked or restricted vent, improper venting, or a malfunctioning inducer
Faulty pressure switch or inducer blower that prevents safe inducer operation
Restricted airflow from a dirty air filter, closed registers, or a failing blower motor
Control board fault or damaged wiring harness leading to incorrect signals
Condensate trap or drain problems causing a safety shutoff in some models
Thermostat problems or miswiring that produce incorrect temperature readings

Step-By-Step Troubleshooting For Code 59

Safety first: switch off power to the furnace at the service disconnect or breaker. If you smell gas or hear a hissing odor, evacuate the area and contact emergency services.
Verify thermostat settings and operation. Ensure the thermostat is set to heat, to a higher temperature than the current room temperature, and that the thermostat has fresh batteries if it uses them. Confirm no recent changes in wiring or settings that could trigger code 59.
Reset the furnace. After turning off power, wait 30–60 seconds and restore power. Some Rheem models require a specific reset sequence; consult the manual for exact steps. A successful reset may clear a temporary lockout, allowing normal startup.
Check the gas supply. Make sure the gas valve is open and that other gas appliances in the home are functioning. If the house has a propane supply, verify the tank level and pressure. If gas flow is interrupted, the furnace cannot ignite safely.
Inspect the air filter and indoor airflow. A dirty or clogged filter reduces airflow, triggering safety limits. Replace the filter if dirty and ensure supply registers are open. Poor airflow can prevent ignition and lead to continued lockouts.
Examine the flame sensor. A dirty or corroded flame sensor can fail to detect the flame, causing the control to shut down. With the furnace powered off, gently remove the flame sensor and clean it with a soft cloth or 400–600 grit emery cloth. Reinstall and retry ignition after a reset.
Assess the ignition system. If the furnace attempts ignition but fails to sustain a flame, the issue may lie with a weak or failing hot‑surface igniter or ignition transformer. Visual inspection of wires and connectors should be performed by a qualified technician; do not handle high‑voltage components unless certified.
Check venting and the condensate system. Look for obstructions in exhaust or intake vents and ensure the condensate drain is clear. A clogged condensate line or improper venting can trigger safety shutoffs, especially in high‑efficiency models.
Test safety switches and controls. The pressure switch, limit switch, and other safety devices must read correctly and respond to the inducer or vent conditions. A persistent problem here usually requires professional service to diagnose electrical or sensor faults on the control board.
Inspect electrical connections. Loose or corroded connections on the furnace control board, gas valve, igniter, flame sensor, or inducer can cause intermittent signals and lockouts. Ensure all connections are clean, tight, and free of corrosion.
If code 59 persists after these steps, document the exact sequence of events, any strange odors, and recent changes to the system. A professional HVAC technician can perform advanced diagnostics, often using a furnace diagnostic tool to read the control board’s fault codes beyond 59.

Important Safety Precautions

Never bypass safety switches or ignition controls. If ignition components show signs of damage, burning smells, or sparked connectors, shut off the system and contact a licensed technician. Regular maintenance by a trained pro reduces the likelihood of persistent Code 59 and helps preserve system efficiency and safety.

Safety Considerations And When To Call A Pro

Code 59 can indicate a serious fault that affects ignition, flame detection, or venting safety. If the homeowner is uncomfortable with gas systems, or if any step reveals a gas odor, engage emergency services and leave the area. For most households, persistent Code 59 after basic troubleshooting requires a licensed HVAC technician who can perform a full diagnostic, verify gas pressure, test pressure switches, inspect the inducer and venting, and replace faulty components. If the furnace is under warranty, contact the manufacturer or an authorized service provider to avoid voiding coverage.

Documentation of the model, serial number, and a clear description of symptoms helps the technician diagnose faster. In some Rheem models, firmware or control board updates may be necessary to resolve fault codes. Avoid DIY fixes on high‑voltage or gas components to prevent injury or property damage.

Maintenance Tips To Prevent Error Code 59

Schedule annual professional maintenance. A yearly inspection helps identify ignition, flame detection, and venting issues before they trigger Code 59.
Replace air filters regularly. A clean filter promotes stable airflow and reduces strain on the blower and inducer.
Inspect and clean flame sensors during routine service. Clean sensors can prevent false lockouts.
Ensure proper venting and exhaust. Clear any debris blocking vents and verify that outdoor exhausts are unobstructed.
Test and verify safe gas operation. If gas odors are detected, contact the utility or a licensed tech immediately.
Keep the furnace area clear. Remove clutter around the unit to ensure adequate combustion air and ease of servicing.
Track refrigerant and electrical components. For homes with integrated systems or heat pumps, ensure refrigerant levels and electrical connections remain within specifications.

Models, Warranty, And Documentation

Because Rheem uses different control boards and feature sets across models, Code 59 definitions can vary. Owners should consult the specific model’s user manual or Rheem’s official website for model‑specific fault code sheets. If the unit is under warranty, contacting an authorized service provider is advised to preserve coverage. Record the model, serial number, and firmware version when seeking support, as this information speeds up diagnostics and parts replacement when needed.