Rheem Furnace Ignition Failure Troubleshooting and Repair Guide

The following guide helps homeowners diagnose and resolve a Rheem furnace ignition failure with practical troubleshooting steps, common causes, safety tips, and repair options. It focuses on clear, actionable information to restore reliable heating while explaining when professional service is advised.

Symptom	Likely Cause	Typical Fix
Unit Won’t Light	Faulty ignitor or ignition control	Test/replace ignitor or control board
Intermittent Ignition	Dirty flame sensor or gas valve issues	Clean sensor; inspect gas valve/pressure
Clicking But No Flame	No gas supply or blocked burner	Check gas line; clean burners
Error Codes Or LED Flashing	Control board diagnostic fault	Read code; follow Rheem troubleshooting chart

How Rheem Furnace Ignition Systems Work

Modern Rheem furnaces typically use direct spark ignition (DSI) or hot surface ignition (HSI). Both systems receive a call for heat from the thermostat and follow a timed sequence: inducer motor starts, pressure switch verifies airflow, ignition sequence begins, gas valve opens, flame establishes, and flame sensor confirms combustion. Ignition failure occurs when any step in this sequence is interrupted.

Common Causes Of Rheem Furnace Ignition Failure

Identifying the root cause requires systematic checks because multiple components interact during ignition. Common causes include: failed ignitor, dirty or faulty flame sensor, gas supply problems, clogged burners, malfunctioning control board, pressure switch or inducer motor failures, faulty thermostat communication.

Failed Ignitor

HSI elements crack or burn out after cycles; spark ignitors wear or fail electrically. A visually damaged or glowing ignitor that won’t light the gas is a frequent cause of complete ignition failure.

Dirty Or Faulty Flame Sensor

The flame sensor detects the presence of flame. When it is coated with carbon or oxidation, it cannot sense flame reliably, causing the control board to shut off gas after a brief ignition attempt.

Gas Supply And Burner Issues

Closed gas valves, disrupted gas service, low gas pressure, or clogged burner ports prevent adequate fuel flow. The ignitor may glow or spark but no flame forms.

Control Board And Diagnostic Failures

The furnace control board coordinates the sequence and logs error codes. A failed control board or one reporting persistent diagnostic faults can prevent ignition or create intermittent behavior.

Inducer Motor And Pressure Switch Problems

If the inducer motor fails or the pressure switch does not close, the system aborts ignition for safety. These parts ensure proper venting and airflow before allowing gas flow.

Diagnostic Checklist For Homeowners

For safety, turn off power and gas before inspecting internal components. If the homeowner is uncomfortable, contact a licensed HVAC technician. The checklist below helps narrow causes before repairs or parts replacement.

• Confirm thermostat settings and batteries, and that the unit is set to heat.
• Check the furnace’s LED diagnostic code (usually behind the access panel) and note flashing patterns.
• Listen for the inducer motor; observe whether burners attempt to ignite.
• Inspect the ignitor visually for cracks or damage (HSI) or weak spark (DSI).
• Clean the flame sensor with a non-abrasive pad if soot or buildup is present.
• Verify the gas valve is open and other gas appliances are working to rule out supply issues.
• Check the air filter and ensure vents and returns are unobstructed to avoid safety shutoffs.

Testing Key Components

Basic tests can confirm component status. Use proper safety gear and a multimeter rated for HVAC work. If unsure, stop and call a technician.

Ignitor Testing

For HSI: visually inspect the ceramic element for cracks and measure resistance. Typical HSI resistance ranges vary by model (often tens to hundreds of ohms). A completely open circuit indicates failure. For DSI: observe spark intensity and verify the high-voltage lead is intact.

Flame Sensor Testing

Remove the sensor and clean with a fine abrasive pad. Reinstall and run the furnace. If ignition stabilizes, the sensor was the cause. For electrical testing, measure microampere signal to the control board while the flame is present; low or zero microamps indicates a bad sensor or wiring issue.

Gas Valve And Pressure Checks

Confirm the gas valve receives the proper DC voltage (commonly 24VAC for modern systems) when the control board calls for heat. If voltage is present but no gas flow, the valve may be stuck. Measuring manifold pressure requires a manometer and professional skill.

Control Board And Error Codes

Record the LED flash sequence and consult the Rheem service manual or label inside the furnace. Error codes point to specific subsystems (pressure switch, flame rollout, limit switch, etc.). A consistent code simplifies diagnosis significantly.

Step-By-Step Troubleshooting Sequence

This ordered sequence reduces time and avoids unnecessary part replacements. Follow from top to bottom until ignition is restored.

1. Confirm thermostat operation and that the furnace has power and gas supply.
2. Replace or clean the air filter and restore airflow; attempt a restart.
3. Check and clean the flame sensor; test for improved ignition.
4. Inspect the ignitor visually; replace if cracked or not glowing/sparking.
5. Read control board LED codes and follow indicated troubleshooting steps.
6. Verify inducer motor operation and pressure switch closure.
7. Check gas valve wiring and voltage during a call for heat.
8. If multiple components appear to fail simultaneously, suspect control board or power-supply issues.

When To Replace Parts Versus Clean Or Reset

Cleaning often resolves flame sensor and burner port issues. Ignitors and gas valves require replacement when failed. Control boards should be replaced only after verifying upstream components are functioning because boards often fail due to other faulty parts. Replace parts based on diagnostic evidence rather than guesswork to reduce costs.

Typical Repair Costs And Timeframes

Costs vary by region and unit model. Typical ranges: flame sensor replacement $80–$200, ignitor $100–$350, gas valve $200–$500, inducer motor $200–$500, control board $300–$800. Labor can add $100–$300. Emergency or weekend service raises prices. Always request an itemized quote and warranty information.

Safety And Regulatory Considerations

Gas and electrical systems pose hazards. Turn off power and gas before service, and never attempt gas valve repairs without proper certification. Local codes may require licensed HVAC or gas-fitting professionals for certain repairs or permit work.

Preventive Maintenance To Avoid Ignition Failures

Routine maintenance extends furnace life and reduces ignition failures. Recommended actions include annual professional tune-ups, changing filters every 1–3 months, keeping combustion air and vents clear, and scheduling burner and heat-exchanger inspections. Regular checks of the flame sensor and ignitor during maintenance visits prevent most common ignition issues.

When To Call A Professional

Contact a licensed HVAC technician if any of the following occur: repeated unsuccessful ignition attempts, gas odor near the furnace, error codes that are not resolved by basic checks, failed gas valve, suspected control board failure, or lack of comfort from intermittent operation. Professionals have tools for safe gas-pressure measurement, leak testing, and detailed electronic diagnostics.

Choosing Replacement Parts And Warranties

Use OEM Rheem parts or reputable aftermarket equivalents. Verify part numbers against the furnace model plate. Ask about warranties on parts and labor; extended warranties for control boards or heat exchangers may be available. Keep service records and receipts for future reference and warranty claims.

Useful Resources And Documentation

Rheem owner manuals and service bulletins provide model-specific diagnostics and error-code charts. Manufacturer technical support lines and certified contractor directories assist with complex issues. Homeowners should retain the furnace model and serial number for quick access to accurate information.

Summary Of Key Troubleshooting Tips

• Start Simple: Check thermostat, power, gas, and filter first.
• Read Codes: Control board LED codes dramatically speed diagnosis.
• Clean Before Replace: Flame sensor cleaning often solves intermittent failures.
• Test Safely: Use proper tools and PPE; stop and call a pro if unsure.
• Document Repairs: Save receipts and part numbers for warranty and future reference.

For persistent Rheem furnace ignition failure issues, combining methodical troubleshooting with timely professional service ensures safe, efficient restoration of heating performance.