The Rheem furnace blinking light codes are a built-in diagnostic tool that helps identify system problems quickly and accurately. This guide explains the most common blink patterns, what they mean, and practical troubleshooting steps homeowners and technicians can follow to restore safe operation.
| Blink Pattern | Meaning | Common Causes |
|---|---|---|
| 1 Flash | Pressure Switch Open | Blocked vent, failed switch, inducer issue |
| 2 Flashes | Pressure Switch Closed/Short | Shorted switch, wiring harness damage |
| 3 Flashes | Open Limit Or Flame Rollout | Restricted airflow, dirty filter, cracked heat exchanger |
| 4 Flashes | Flame Loss/Flame Sensitivity | Ignitor failure, gas valve problem, flame sensor dirty |
| 5 Flashes | Open High Limit | Overheating, blower failure, blocked return |
| 6 Flashes | Ignition Lockout | Repeated ignition failures, gas supply issues |
How Rheem Furnace Diagnostic Lights Work
Rheem furnaces use an LED or indicator light to communicate system status through timed blink patterns. Each pattern corresponds to a diagnostic code stored in the control board. Technicians interpret these codes to pinpoint the likely subsystem causing the fault.
Key Point: The blink code is a starting point, not a definitive repair list. Proper diagnosis requires inspection, testing, and verification of components related to the indicated code.
Common Rheem Blink Codes And Their Meanings
1 Flash: Pressure Switch Open
One blink typically indicates the pressure switch did not close during the inducer motor startup sequence. The pressure switch proves the inducer is moving combustion air properly.
Common causes include a clogged vent or blocked combustion air intake, a weak inducer motor, kinked PVC vent pipe, or a failing pressure switch diaphragm.
Troubleshooting Steps For 1 Flash
- Inspect intake and exhaust vents for obstructions, bird nests, or debris.
- Verify inducer motor runs when the furnace attempts to start.
- Check vent piping for disconnections or holes and ensure proper slope if required.
- Measure the pressure switch with a multimeter when the inducer runs; it should close.
- Replace the pressure switch if it fails continuity testing.
2 Flashes: Pressure Switch Closed/Shorted
Two flashes can indicate the pressure switch remains closed or is shorted when it should be open, signaling a wiring short or a stuck switch.
Causes include a shorted harness, foreign material in switch tubing, or a defective switch stuck closed.
Troubleshooting Steps For 2 Flashes
- Inspect switch tubing for moisture or debris and clear or replace tubing if contaminated.
- Check wiring for frays, pinched insulation, or rodent damage causing shorts.
- Disconnect the pressure switch leads and test continuity; a switch that reads closed at rest is defective.
3 Flashes: Open Limit Or Flame Rollout
Three flashes usually point to an open limit switch or a flame rollout condition. This is a safety response to high heat near the burner box or restricted airflow.
Typical causes are dirty filters, blocked return ducts, closed registers, or a cracked heat exchanger causing abnormal flame behavior.
Troubleshooting Steps For 3 Flashes
- Replace the air filter and inspect the return and supply registers for blockages.
- Check the blower motor operation; a failing blower can cause overheating and tripping limits.
- Inspect the heat exchanger visually for cracks or signs of corrosion; a certified technician should perform thorough inspection and CO testing.
- Test limit switches for continuity and replace if open under normal conditions when cool.
4 Flashes: Flame Loss Or Sensitivity
Four flashes generally indicate flame detection problems such as flame sensor failure, weak flame due to gas pressure, or ignition issues that cause inconsistent flame sensing.
Common causes include a dirty flame sensor, weak gas supply, or a failing gas valve or ignitor assembly.
Troubleshooting Steps For 4 Flashes
- Carefully clean the flame sensor rod with fine emery cloth to remove oxidation and carbon buildup.
- Inspect and test the hot surface ignitor for cracks and measure resistance against manufacturer specs.
- Confirm adequate gas supply and pressure; consult a licensed technician for gas valve testing.
- Replace the flame sensor if cleaning does not restore proper flame detection.
5 Flashes: Open High Limit
Five blinks denote that the high limit switch opened, indicating excessive heat in the heat exchanger or restricted airflow causing elevated temperatures.
Causes may include clogged filters, closed or blocked supply vents, or a malfunctioning blower motor that fails to move sufficient air.
Troubleshooting Steps For 5 Flashes
- Replace or clean the air filter and ensure supply and return vents are open and unobstructed.
- Test blower motor, capacitor, and relay for proper operation; replace faulty components to restore airflow.
- Inspect ductwork for blockages or severe constrictions that reduce airflow.
6 Flashes: Ignition Lockout
Six flashes indicate ignition lockout after multiple unsuccessful ignition attempts. This is a safety feature to prevent gas buildup and unsafe operating conditions.
Typical causes include failed ignitor, defective gas valve, weak flame signal, or primary control issues.
Troubleshooting Steps For 6 Flashes
- Allow the control to reset or manually reset per the unit instructions, then observe ignition cycles.
- Test ignitor for continuity and proper resistance; replace if cracked or out-of-spec.
- Inspect gas valve operation and gas line supply; a licensed professional should test gas pressures and valve actuation.
- Check flame sensor and control board connections for corrosion or loose wiring.
Less Common Blink Codes And Special Cases
Some Rheem controls support additional patterns or steady codes indicating issues like system lockout, outdoor temperature sensor faults, or auxiliary heat problems in heat pump hybrids.
Key Tip: Always consult the specific model’s service manual or the furnace data plate for manufacturer-specific code definitions, as interpretations can vary across control boards.
Safe Diagnostic Practices And Tools
Working on gas furnaces requires safety precautions. Turn off power and gas before inspecting internal components unless instructed to observe live behavior. If uncertain, hire a licensed HVAC technician.
Recommended tools include a multimeter, manometer for gas pressure testing, non-contact voltage tester, screwdrivers, and a replacement filter. For flame sensing checks, a combustion analyzer and CO meter provide safety verification.
When To Call A Professional
Call a licensed HVAC technician if the blink code indicates potential heat exchanger cracks, repeated ignition lockouts, gas valve issues, or if the homeowner is uncomfortable performing electrical or gas-related tests.
Safety-Related Codes: Any code suggesting flame rollout, heat exchanger damage, or persistent gas-related failures requires immediate professional evaluation.
Preventive Maintenance To Avoid Blink Codes
- Replace air filters every 1–3 months to maintain airflow and reduce limit trips.
- Schedule annual professional tune-ups to inspect heat exchanger, clean burners, and verify safe operation.
- Keep vent terminations clear of debris, snow, and leaves to prevent pressure switch errors.
- Ensure proper thermostat operation and correct wiring to avoid control board misinterpretation of signals.
Model-Specific Variations And How To Find Accurate Codes
Rheem furnaces use different control boards across product lines. The same blink pattern can mean slightly different things depending on the control version.
Locate the unit’s model and serial number on the data plate, then download the specific service manual from Rheem’s official website or consult the manual included with the unit to confirm exact blink code definitions.
Example Diagnostic Workflow For A 1-Flash Fault
1) Observe and note the blink pattern and any error history. 2) Check vents and inducer operation visually. 3) Measure pressure switch continuity while inducer runs. 4) Repair vent obstruction or replace pressure switch as indicated. 5) Test-run the furnace to confirm resolution.
Recordkeeping And Reporting For Technicians
Technicians should document blink patterns, component tests, and repairs in service records. This helps identify intermittent faults and recurring failures that may indicate deeper system issues such as control board degradation or systemic airflow restrictions.
Frequently Asked Questions
Can Resetting The Furnace Clear Blink Codes?
Resetting can temporarily clear codes, but persistent faults will return. Resetting is useful for confirming if a transient condition caused the code, but proper diagnosis is required for lasting repairs.
Are Blink Codes The Same Across All Rheem Furnaces?
Not always. Although many codes are consistent, variations exist between control boards and models. Always verify using the model-specific service literature.
Is It Safe To Continue Using The Furnace With A Blink Code?
Some codes indicate minor issues; others suggest unsafe conditions. If the code points to flame rollout, cracked heat exchanger, gas valve failure, or repeated ignition lockouts, discontinue use and call a professional immediately.
Resources And References
Owners and technicians should refer to Rheem’s official service manuals, the product data plate on the furnace, and local codes for gas appliance safety. Certified HVAC training materials and manufacturer troubleshooting guides provide authoritative procedures for diagnosis and repair.
Final Note: Rheem furnace blinking light codes are a powerful troubleshooting aid. Proper interpretation, careful testing, and timely maintenance enable safe, efficient operation and can prevent costly failures.