Introduction
Rheem furnaces are equipped with onboard diagnostic systems that help identify operating problems before they become more serious. When the furnace detects an abnormal condition, the integrated control board displays an error code using an LED indicator or other diagnostic display, depending on the furnace model. These codes provide valuable information that can help homeowners and HVAC technicians identify the source of a problem more quickly.
Most Rheem furnaces use LED blink sequences or numeric fault codes to communicate operating conditions. Some codes indicate normal operation, while others identify issues involving ignition, flame sensing, airflow, venting, safety switches, condensate drainage, or internal control board faults. Because Rheem has produced many furnace models over the years, the exact meaning of an error code can vary depending on the model and control board installed in the equipment.
This guide serves as a central index for Rheem furnace error codes published on HVACFaultFinder.com. Each code links to a dedicated troubleshooting page with a detailed explanation of what the code means, common causes, safe homeowner inspections, and guidance on when professional diagnosis is recommended.
If you are unsure which Rheem furnace model you own, begin by locating the model number on the equipment data plate inside the blower compartment or on the cabinet. Using the correct model information helps ensure that you reference the appropriate diagnostic information for your furnace.
Rheem Furnace Error Code Index
| Error Code | Meaning |
| 1 Blink | Ignition Failure |
| 2 Blinks | Pressure Switch Stuck Closed |
| 3 Blinks | Pressure Switch Stuck Open |
| 4 Blinks | High Limit Open |
| 5 Blinks | Flame Rollout Switch Open |
| 10 | One-Hour Lockout |
| 11 | Failed Ignition |
| 12 | Low Flame Sense |
| 13 | Flame Lost After Ignition |
| 14 | Unexpected Flame |
| 20 | Twinning Communication Fault |
Common Rheem Furnace Problems
While every error code identifies a specific operating condition, many of them fall into a handful of common categories.
Ignition Problems
Ignition-related codes typically indicate that the burners failed to light or that the furnace was unable to establish a stable flame. Possible causes include ignition component failures, gas supply issues, contaminated flame sensors, or burner problems.
Related codes include:
- 1 Blink
- 10
- 11
- 12
- 13
- 14
Pressure Switch Problems
Pressure switch faults usually indicate that the furnace cannot verify proper airflow through the venting system before ignition. These codes often result from blocked vents, condensate drainage issues, damaged pressure tubing, inducer motor problems, or pressure switch failures.
Related codes include:
- 2 Blinks
- 3 Blinks
High Temperature Safety Devices
Limit switches and rollout switches protect the furnace from overheating or unsafe burner conditions. These safety devices should never be bypassed.
Related codes include:
- 4 Blinks
- 5 Blinks
Control Board and Communication Faults
Some diagnostic codes indicate problems within the furnace’s electronic controls or communication between components.
Related codes include:
- 20
Frequently Asked Questions
Where is the diagnostic LED located?
On most Rheem furnaces, the diagnostic LED is visible through a viewing window on the blower compartment door or directly on the integrated furnace control board behind the access panel.
Can I reset a Rheem furnace?
Many faults clear automatically after the underlying problem is corrected. While cycling power may temporarily clear some codes, repeatedly resetting the furnace without addressing the root cause can result in additional lockouts or repeated failures.
Are all Rheem furnace error codes the same?
No. Rheem has used different integrated furnace controls across multiple product lines. Always verify your furnace model before relying on a diagnostic code description.
Should I replace the control board if I see an error code?
Not necessarily. Most diagnostic codes identify problems with another component rather than a failed control board. Proper diagnosis should always identify the underlying cause before replacing parts.
Related Troubleshooting Guides
- Flame Sensor Troubleshooting Guide
- Pressure Switch Troubleshooting Guide
Safety Reminder
Many furnace error codes involve gas combustion, electrical components, or built-in safety controls. Homeowners can safely inspect items such as air filters, vent terminations, and visible wiring, but gas valves, ignition systems, pressure testing, and electrical diagnostics should be performed only by qualified HVAC professionals. If you smell gas or suspect unsafe furnace operation, leave the area immediately and contact your gas utility or emergency services from a safe location.