Rheem Furnace Error Code 13 Troubleshooting and Fixes

The Rheem furnace error code 13 indicates an ignition or flame-related problem that prevents the system from operating normally. This article explains the meaning, common causes, step-by-step troubleshooting, and safe repair or replacement options to help homeowners diagnose and respond effectively.

Item	Quick Summary
Error Code	13 — Ignition/Flame Failure
Common Causes	Dirty ignitor, faulty flame sensor, gas valve issue, blocked vent, control board fault
Risk Level	Moderate — safety systems prevent operation; professional help often required
DIY Possible?	Yes for cleaning/reseating components; no for gas valve/electrical control repairs
When To Call Pro	Persistent error, gas valve/electrical issues, sensor replacement, combustion testing

What Error Code 13 Means On A Rheem Furnace

Error code 13 on many Rheem and Ruud furnaces commonly indicates an ignition or flame failure event detected during the start sequence. The control board attempts ignition but does not detect a sustained flame, so it locks out further operation to protect the system.

This code Is A Safety Response — the furnace control prevents continuous ignition attempts to avoid gas accumulation or unsafe operation.

How The Furnace Ignition Sequence Works

Understanding the sequence helps identify where a failure may occur. Typical steps include thermostat call for heat, inducer motor start, ignitor heat or spark, gas valve opening, flame establishment, and flame sensor confirmation to continue operation.

If any step fails, the control board times out and may display code 13. Common failure points are the ignitor, flame sensor, gas valve, venting, or the control board itself.

Common Causes Of Error Code 13

Several issues can trigger the code. The most frequent causes are: dirty or weak flame sensor, failed ignitor, gas supply or valve problem, blocked vent/combustion air issue, or control board/sensor wiring faults.

• Flame Sensor: Carbon buildup prevents flame current detection.
• Ignitor: Cracked or weakened hot surface ignitors fail to glow hot enough.
• Gas Valve/Gas Supply: Low pressure, closed valve, or faulty valve prevents gas flow.
• Venting/Combustion Air: Obstructions or pressure switch failures stop safe ignition.
• Control Board/Wiring: Shorted or loose connections cause false readings or failures.

Safety Precautions Before Troubleshooting

Always prioritize safety. Turn off power to the furnace at the breaker before accessing internal components. If there is a gas smell, evacuate the home and contact the gas company immediately. Only qualified technicians should handle gas valve replacement, gas pressure adjustments, or control board repairs.

Do Not Attempt high-voltage or gas-system repairs without certification. Simple cleaning and visual inspections can be done safely by homeowners.

Step-By-Step Troubleshooting Guide

1. Verify Error And Reset The Furnace

Record the displayed code and sequence of LED blinks if available. Try a simple reset by turning the furnace power off for 30 seconds and back on. If the code clears but returns, proceed with deeper troubleshooting.

2. Check Thermostat And Settings

Confirm the thermostat is set to heat and the temperature is above the setpoint. Replace thermostat batteries and inspect wiring connections for tightness and corrosion.

3. Inspect Air Filter And Combustion Air

A clogged air filter or restricted return can affect combustion. Replace dirty filters. Verify outdoor combustion air vents and intake are clear of debris, nests, or snow.

4. Observe The Ignition Sequence

With power restored, watch the sequence: inducer motor, pressure switch closure, ignitor glow or spark, gas valve operation, and flame establishment. Note which step fails; this narrows the likely faulty component.

5. Clean The Flame Sensor

The flame sensor often causes code 13. Remove the sensor (usually one screw) and gently clean the metal rod with fine emery cloth or steel wool to remove carbon. Reinstall and test. Cleaning is a common, effective fix.

6. Inspect And Test The Ignitor

For hot surface ignitors, look for cracks or white and dark deposits. A cracked or brittle ceramic element indicates failure and requires replacement. Do not touch the surface with bare hands as oils shorten life.

7. Check Gas Supply And Valve

Ensure the gas shutoff valve to the furnace is open and other gas appliances are functioning. If the valve is open but no gas is flowing to the burner, stop and call a licensed technician. A qualified technician will test manifold pressure and the gas valve solenoid.

8. Verify Venting And Pressure Switch

Ensure exhaust vents are unobstructed and the vent pipe is intact. A blocked vent or failed inducer motor can prevent the pressure switch from closing, stopping the ignition. Inspect and clear any blockages.

9. Inspect Wiring And Control Board

Loose, corroded, or damaged wires between the flame sensor, ignitor, and control board can mimic component failures. Tighten connections and look for burnt traces on the control board. Replace the control board only after ruling out sensors and actuators.

When To Replace Parts

Replace the flame sensor if cleaning fails to restore reliable operation. Replace the ignitor if it shows physical damage or fails continuity testing with a multimeter. Replace the gas valve or control board only after professional diagnosis confirms their failure.

Keep OEM Parts In Mind — using manufacturer-recommended parts preserves reliability and warranty coverage.

Cost Estimates And Timeframes

Costs vary by repair type. Cleaning a flame sensor is low-cost (parts: minimal; time: 15–30 minutes). Ignitor replacement typically ranges from $150–$350 including parts and labor. Gas valve or control board replacements often range from $400–$1,200 depending on model and labor rates.

Turnaround time depends on technician availability and part lead times but minor repairs often complete the same day.

When To Call A Professional

Contact a licensed HVAC technician if error code 13 persists after basic cleaning, when gas valve or control board replacement is likely, or if the homeowner detects gas odor or electrical burning. Professionals perform combustion analysis, gas pressure checks, and safe repairs that require certification.

Immediate Professional Help Needed if repeated ignition attempts occur, if there is a strong gas smell, or if the furnace displays multiple fault codes.

Preventive Maintenance To Avoid Error Code 13

• Schedule annual professional furnace inspections and tune-ups before the heating season.
• Replace air filters every 1–3 months to maintain airflow and combustion efficiency.
• Keep intake and exhaust vents clear and inspect for animal nests or debris.
• Perform periodic visual checks of the furnace interior for soot, corrosion, or wiring problems.
• Consider adding a service contract for priority service and routine cleaning of flame sensors and burners.

Model Variations And Diagnostic Differences

Rheem uses model-specific control boards and diagnostic codes. Some models may display code 13 as an LED blink pattern or a different numeric logic. Always consult the furnace’s installation and service manual for model-specific diagnostics and error code charts.

If the manual is unavailable, Rheem’s website and customer support provide documentation and replacement part numbers for many models.

Frequently Asked Questions (FAQs)

Can A Dirty Flame Sensor Cause Code 13 Every Time?

Yes. Carbon buildup is a frequent and recurring cause of flame detection failure. Regular cleaning can prevent repeated lockouts, but a failing sensor should be replaced.

Is It Safe To Reset The Furnace Frequently?

Occasional resets to clear a transient fault are acceptable, but frequent resets indicate an unresolved issue. Continuous resets can stress components and should prompt professional evaluation.

How Long Does It Take A Technician To Fix Code 13?

Simple fixes like cleaning the flame sensor often take under an hour. Complex repairs involving gas valves or control boards take longer due to diagnosis, parts, and safety testing.

Will Replacing The Thermostat Fix Error Code 13?

Not directly. Thermostats can cause improper calls for heat but do not cause ignition failures. Replace the thermostat only if communication or wiring problems are identified.

Useful Resources And Further Reading

Official Rheem product manuals, the National Fire Protection Association (NFPA) combustion safety guidelines, and EPA/DOE HVAC maintenance recommendations are reliable resources for homeowners and technicians seeking deeper technical guidance.

Tip: Saving the furnace model and serial number before calling support speeds up diagnosis and parts identification.

Action	Who Should Do It
Clean Flame Sensor	Homeowner or Technician
Replace Ignitor	Technician Recommended
Gas Valve Or Control Board Replacement	Licensed HVAC Technician
Combustion Testing	Licensed Technician

For persistent Rheem furnace error code 13 issues, combining basic homeowner troubleshooting with timely professional service ensures safe, efficient heating and prevents recurring lockouts.