Rheem / Ruud Furnace & AC Error Codes
Below is a complete list of Rheem / Ruud furnace and air conditioner diagnostic error codes (also applies to Rheem, Ruud, WeatherKing). Each code includes what it means, safe DIY checks you can try, when to call a professional, and estimated repair costs.
How to Read Rheem / Ruud Error Codes
Look through the sight glass on the furnace access panel. On standard models, count the LED blinks before the pause and repeat. On newer models with a digital display, read the code directly. A slow steady blink (1 per second) means normal standby. Match the flash count to the error code chart on the label inside the access panel. Note: Rheem and Ruud furnaces are made by the same manufacturer and share identical diagnostic codes.
LED Location: The diagnostic LED is on the control board, visible through the sight glass on the lower front access panel. Newer models may have a digital display showing codes and operating status.
Code Format: Single-digit flash code: count the number of LED blinks in each repeating sequence. Some newer models have a digital display showing alphanumeric codes (e.g., 'H' for heating, '0' for standby). Rheem and Ruud use identical codes as they are the same manufacturer.
Safety Warning
1 emergency code(s) require immediate professional attention. 6 high-urgency code(s) should be addressed promptly. If you smell gas, hear unusual sounds, or see sparks, turn off the system and call a professional immediately.
Quick Navigation — 12 Error Codes
Rheem / Ruud Slow Blink (1 per second): Normal operation — standby
Low UrgencyThe furnace is powered on and operating normally in standby mode. It is waiting for the thermostat to call for heat. On models with a digital display, this may show '0' for standby.
Common Causes
- Thermostat is not calling for heat (normal condition)
- Room temperature is at or above the thermostat set point
DIY Troubleshooting Steps
- No action needed — this is a normal status
- If you need heat, check your thermostat to make sure it is set to HEAT and the temperature is set higher than the room temperature
Call a professional when: The furnace shows normal standby but does not respond when the thermostat calls for heat.
Rheem / Ruud 1 Blink: Ignition failure — soft lockout (1 hour)
Medium UrgencyThe furnace failed to ignite and has entered a soft lockout. It will automatically retry after approximately 1 hour, or you can manually reset it sooner. This is a temporary lockout that clears on its own.
Common Causes
- Dirty or corroded flame sensor not detecting the flame
- Weak or failing hot surface igniter
- Gas supply interruption (closed valve, low pressure)
- Intermittent gas valve issue
DIY Troubleshooting Steps
- Clean the flame sensor with fine steel wool or emery cloth (turn off power first) — this is the most common fix for this code
- Verify the gas supply is on — check the manual shut-off valve near the furnace
- Reset the furnace early by turning power off for 30 seconds, then back on
Call a professional when: The code keeps appearing after cleaning the flame sensor and verifying gas supply. A technician can test the igniter resistance, flame sensor signal, and gas pressure.
Rheem / Ruud 2 Blinks: Pressure switch stuck open
Medium UrgencyThe pressure switch did not close when the inducer motor activated. The inducer is running but not creating enough draft to close the pressure switch, or the switch itself has failed.
Common Causes
- Blocked exhaust or intake vent pipe (ice, snow, debris, bird nests)
- Clogged condensate drain causing water backup (high-efficiency models)
- Cracked, kinked, or disconnected pressure switch rubber tubing
- Weak or failing inducer motor
DIY Troubleshooting Steps
- Check exhaust and intake vent pipes outside for blockages — clear any ice, snow, or debris
- Inspect the small rubber hose connecting the pressure switch for cracks, kinks, or water inside — disconnect one end and blow it clear
- Check the condensate drain for clogs on high-efficiency furnaces
Call a professional when: The vents are clear and the hose is intact but the code persists. The inducer motor may be weak, or the pressure switch may need replacement.
Rheem / Ruud 3 Blinks: Limit switch or rollout switch open
High UrgencyThe main high-temperature limit switch or the flame rollout safety switch has opened. The limit switch opens when the furnace overheats. The rollout switch opens when flames are detected outside the burner area.
Common Causes
- Dirty or clogged air filter causing overheating (limit switch trip — most common)
- Blocked supply or return registers restricting airflow
- Failed blower motor or bad capacitor
- Cracked heat exchanger or blocked vent causing flame rollout
DIY Troubleshooting Steps
- Replace the air filter immediately
- Open all supply and return vents and registers in the home
- Verify the blower motor is running during the heating cycle
Call a professional when: The code returns after changing the filter and opening vents. If this is a rollout switch issue (not a limit switch), this is a serious safety concern that could indicate a cracked heat exchanger and carbon monoxide risk.
Rheem / Ruud 4 Blinks: Pressure switch stuck closed
Medium UrgencyThe pressure switch is in the closed position when the inducer motor is not running. The switch should be open when there is no draft. This indicates the switch contacts are stuck or there is a wiring short.
Common Causes
- Defective pressure switch with welded or stuck contacts
- Short circuit in the pressure switch wiring
- Residual vacuum in the vent system holding the switch closed
- Water trapped in the pressure switch or hose
DIY Troubleshooting Steps
- Check the rubber tubing for trapped water — disconnect one end and drain it
- Try resetting the furnace by cycling power off for 30 seconds
Call a professional when: This code typically requires a technician to replace the pressure switch. It is a safety device that must not be bypassed.
Rheem / Ruud 5 Blinks: Flame sensed with gas valve off
EmergencyThe flame sensor is detecting a flame when no flame should be present (gas valve is off). This can indicate a dangerous gas leak past the valve. On some boards with twinning capability, 5 blinks can also indicate a twinning circuit failure.
Common Causes
- Leaking gas valve allowing gas past when closed
- Gas valve stuck in open position
- Defective flame sensor reading false flame signal
- Twinning circuit error (on twinned systems only)
DIY Troubleshooting Steps
- If you smell gas, evacuate immediately and call 911 or your gas company from outside the home
- Turn off the gas supply valve to the furnace as a precaution
Call a professional when: Always call a professional. A gas valve that leaks when closed is a serious fire and explosion risk. Do not operate the furnace until it is inspected.
Rheem / Ruud 6 Blinks: Line voltage polarity reversed or rollout switch open
High UrgencyOn many Rheem/Ruud boards, 6 blinks indicates the 115V AC power polarity is reversed (hot and neutral wires swapped). On some board revisions, it indicates the rollout switch is open. Check the label inside your access panel for your specific model.
Common Causes
- Hot and neutral wires reversed at the furnace connection or disconnect
- Flame rollout detected (on certain board revisions)
- Recent electrical work affecting the furnace circuit
- Faulty disconnect or outlet wiring
DIY Troubleshooting Steps
- If recent electrical work was performed, contact the electrician
- Check the exhaust vent for blockages if rollout is suspected
- Do not attempt to rewire the furnace yourself
Call a professional when: Always call a professional. Both reversed polarity and flame rollout require professional correction.
Rheem / Ruud 7 Blinks: Ignition lockout — too many retries (hard lockout)
High UrgencyThe furnace has entered a hard lockout after exhausting its maximum number of ignition retry attempts. Unlike the 1-blink soft lockout, this will NOT auto-reset. You must manually reset the furnace by cycling power.
Common Causes
- All the same causes as 1-blink (dirty flame sensor, bad igniter, gas issue) but the problem has persisted through multiple retry cycles
- Persistent gas supply issue
- Failed igniter that worked intermittently
- Gas valve that opens intermittently
DIY Troubleshooting Steps
- Reset the furnace by turning power off for 30 seconds, then back on
- Clean the flame sensor thoroughly (turn off power first)
- Verify gas supply is fully on
Call a professional when: The hard lockout recurs after reset. Multiple failed ignition cycles indicate a persistent problem that needs professional diagnosis — igniter testing, gas pressure measurement, and valve testing.
Rheem / Ruud 8 Blinks: Gas valve circuit failure
High UrgencyThe control board has detected a problem with the gas valve electrical circuit. The valve is not responding correctly to the control signal.
Common Causes
- Loose or corroded wiring at the gas valve terminals
- Defective gas valve solenoid coil
- Failed control board gas valve output relay
- Wiring damage between the board and valve
DIY Troubleshooting Steps
- Turn off power and visually inspect the wiring at the gas valve for loose connections or visible damage
- Try resetting the furnace by cycling power
Call a professional when: This code requires a technician. Gas valve circuits combine electrical and gas hazards and must be diagnosed and repaired by a licensed professional.
Rheem / Ruud 9 Blinks: Igniter circuit fault or grounding problem
High UrgencyThe control board has detected an issue with the hot surface igniter circuit, or there is a grounding problem causing voltage leakage between neutral and the 24V common.
Common Causes
- Cracked or failed hot surface igniter
- Improper or missing furnace ground connection
- Short circuit in the igniter wiring
- Control board igniter relay failure
DIY Troubleshooting Steps
- Visually inspect the igniter through the sight glass for visible cracks
- Check that the furnace ground wire is securely attached
Call a professional when: This code requires professional diagnosis to determine if the issue is the igniter, grounding, or the control board.
Rheem / Ruud 10 Blinks: Line and neutral reversed or blower issue
High UrgencyOn some Rheem/Ruud board revisions, 10 blinks indicates reversed line voltage polarity. On other revisions, it indicates the blower motor did not reach the target speed. Check the label in your access panel.
Common Causes
- Reversed polarity (hot and neutral wires swapped)
- Failing blower motor unable to reach speed
- Dirty blower wheel or clogged filter creating excessive load
- Faulty blower motor wiring
DIY Troubleshooting Steps
- Replace the air filter if dirty
- If electrical work was recently done, contact the electrician
Call a professional when: Call a professional to determine if this is a wiring issue or a blower motor problem. Both require professional diagnosis.
Rheem / Ruud LED Off (no light): No power to the furnace
Medium UrgencyThe diagnostic LED is completely dark, indicating no electrical power is reaching the control board.
Common Causes
- Tripped circuit breaker
- Furnace power switch turned off
- Blown control board fuse
- Damaged power wiring
DIY Troubleshooting Steps
- Check and reset the furnace circuit breaker at the electrical panel
- Locate and verify the furnace power switch is ON
Call a professional when: The breaker keeps tripping or the LED remains off after verifying power is on.
Need Rheem / Ruud Repair in Central Texas?
Texas Temp Masters provides expert HVAC repair for Rheem / Ruud , Rheem, Ruud, WeatherKing, and all major brands in Killeen, Waco, Temple, and surrounding areas. Call (817) 704-0706 for fast, reliable service, or contact us online.
Error code information cross-referenced from manufacturer documentation, HVAC/appliance professional resources, and verified repair databases. Codes can vary by specific model and control board revision. Always verify against your unit's diagnostic label or owner's manual. Repair costs are estimates based on national averages. Last updated February 2026.
Need Emergency HVAC Service?
Don't wait when your heating or cooling system fails. Our licensed technicians provide same-day emergency service throughout Central Texas with guaranteed satisfaction.