If your Rheem furnace is flashing LED codes or throwing error messages, it’s trying to tell you something important about what’s wrong. But decoding those blinks can feel like learning a new language.
With 20+ years in the HVAC industry and as a Rheem Pro Partner, I’ve diagnosed just about every code a Rheem furnace can throw. In this guide, I’ll help you understand exactly what those codes mean, why they happen, and how to fix them.
Common Rheem Furnace Flash Codes at a Glance
Code
Meaning
Severity
1 Flash
Ignition Failure
Moderate
2 Flashes
Pressure Switch Stuck Closed
Moderate
3 Flashes
Pressure Switch Stuck Open
Moderate
4 Flashes
Open Limit Switch
Moderate to High
5 Flashes
Flame Sensed When Off
High
6 Flashes
Rollout Switch Open
Critical
7 Flashes
Ignition Lockout
Moderate
What Are Rheem Furnace Error, Flash, and LED Codes?
Rheem furnaces use a diagnostic LED light system to communicate operational issues. When your furnace detects a problem, it triggers a fault condition and the LED light flashes a specific number of times in a pattern. This flash sequence is essentially a coded message that corresponds to a specific fault.
These codes are most often found on the control board, which is typically behind the blower panel. The number of blinks and the pattern (solid, slow flash, fast flash, etc.) represent different furnace problems, ranging from minor to critical.
Rheem Furnace Flash Codes: What the Blinking Light Means
Normal Operation Codes:
Solid LED On: Furnace has power and is operating normally.
Slow Flash (1 blink/second): Furnace is operating normally but waiting for a call for heat.
Common Error Codes:
1 Flash: Ignition failure. Check gas supply, flame sensor, or ignitor.
2 Flashes: Pressure switch stuck closed. This could be due to a blocked vent or faulty switch.
3 Flashes: Pressure switch stuck open. Common causes: inducer motor issue or pressure switch failure.
4 Flashes: Open limit switch. May be due to overheating or a dirty filter restricting airflow.
5 Flashes: Flame sensed with gas valve off. Possible stuck gas valve or faulty control board.
7 Flashes: Lockout due to too many ignition retries. Furnace will need manual reset.
Tip from Alex: I once serviced a Rheem Classic Plus furnace in Wintersville that threw a 3-flash code. The issue ended up being a bird nest partially blocking the flue pipe. Always check your venting!
Rheem Furnace LED Code Chart
LED Flashes
Meaning
Likely Causes
1
Ignition Failure
Flame sensor, ignitor, gas supply
2
Pressure Switch Closed
Blocked flue, faulty switch
3
Pressure Switch Open
Inducer motor issue, cracked hose
4
Open Limit Switch
Overheating, dirty filter, blower issue
5
Flame Detected When Off
Faulty gas valve, control board
6
Rollout Switch Open
Flame rollout, cracked heat exchanger
7
Ignition Lockout
Gas issues, sensor problems
What Causes Rheem Furnace Error Codes?
Error codes typically appear due to:
Dirty filters or blocked airflow
Ventilation obstructions (like leaves or nests)
Faulty pressure or limit switches
Flame sensor problems
Ignitor or control board malfunctions
These aren’t just nuisances — they can cause system shutdowns, increase energy bills, or even present safety hazards.
Can You Fix These Error Codes Yourself?
Some minor issues can be safely handled by homeowners:
Replacing a dirty air filter
Clearing outdoor exhaust vents
Resetting the furnace (by turning power off for 30 seconds)
However, anything involving gas, flame rollout, or electrical components should be handled by a licensed technician.
Alex’s Advice: In one job near Mingo Junction, a client tried to clean the flame sensor with steel wool and damaged the protective coating. That small mistake cost them a whole new sensor. Use a dollar bill or fine-grit sandpaper, never metal abrasives.
Some minor issues can be safely handled by homeowners:
Replacing a dirty air filter
Clearing outdoor exhaust vents
Resetting the furnace (by turning power off for 30 seconds)
However, anything involving gas, flame rollout, or electrical components should be handled by a licensed technician.
Alex’s Advice: In one job near Mingo Junction, a client tried to clean the flame sensor with steel wool and damaged the protective coating. That small mistake cost them a whole new sensor. Use a dollar bill or fine-grit sandpaper, never metal abrasives.
Why is my Rheem furnace blinking 3 times?
It means the pressure switch is stuck open. Likely causes include a failed inducer motor or blocked condensate line.
How do I reset a Rheem furnace?
Turn off the power at the furnace switch or breaker, wait 30 seconds, then turn it back on. If the issue persists, it may need service.
What does code 57 mean on a Rheem furnace?
Code 57 typically refers to a soft lockout condition. This usually indicates multiple ignition failures in one cycle.
Where is the reset button on a Rheem furnace?
Most Rheem furnaces do not have a dedicated reset button. Power-cycling is the typical reset method.
What do blinking lights on a Rheem 90 Plus furnace mean?
The LED blinks are diagnostic codes. Count the flashes to determine the fault using the chart above.
When to Call for Help
If your Rheem furnace displays codes like 3, 5, or 6 flashes, or if it keeps shutting down despite resets, it’s time to schedule service.
Honest Fix charges a flat diagnostic fee for furnace troubleshooting and repairs. We serve homeowners within 15 miles of Steubenville, OH, including Weirton, WV.
To schedule your service, contact one of our Comfort Guides today.
Other Common Furnace Code Questions
What do error codes mean on a Rheem Criterion II gas furnace?
These follow the same LED flash code system. Refer to the chart above for decoding.
Rheem furnace code 22?
This is typically associated with flame failure or no flame signal detected after ignition. Have the sensor and gas flow checked.
Rheem 90 Plus flashing green light?
A green light flash pattern on the 90 Plus often signals normal operation, but repeated patterns indicate specific faults.
Where is the pressure switch on a Rheem furnace?
Usually mounted near the inducer motor housing. It’s a small round component with rubber tubing connected.
Rheem furnace not turning on — what should I check?
Check the thermostat, breaker, air filter, and any flashing codes. If none of these resolve it, contact a technician.
Summary and Next Steps
Rheem furnaces are built with diagnostic tools to help you identify problems quickly. Whether your unit is flashing a 1 for ignition failure or a 6 for a dangerous flame rollout, knowing what the code means is your first step to staying warm and safe. This guide gives you the information you need to troubleshoot with confidence—and understand when it’s time to call in a pro.
If you’re in the Steubenville or Weirton area and your Rheem furnace is flashing codes, schedule a diagnostic with Honest Fix today. Our Comfort Guides will identify the problem and provide a clear repair path.
