Rheem and Ruud Error Code Systems
Rheem and Ruud furnaces use two separate but overlapping diagnostic systems. The control board LED flashes a blink count (1 through 9 or more) to signal a fault category. Newer models also display a 2-digit numeric code for more precise diagnosis. Ruud furnaces use the exact same code systems. The two brands share the same parent company and identical internal components.
Knowing which code system your furnace uses matters. If you have an older Rheem Classic or Ruud Achiever, you will see only flash codes. If you have a Prestige or Endeavor series, the control board may show both a flash pattern and a 2-digit numeric code.
Rheem Flash Code Reference Table
Locate the furnace control board. The diagnostic LED sits on the board behind the lower access panel. Count the number of blinks in each sequence. The board pauses between sequences. A steady blinking pattern with no pause between counts (continuous) means a different fault than the counted blinks below.
| Flash Count | Meaning | Likely Cause |
|---|---|---|
| 1 flash | No flame sense after gas valve opens | Dirty flame sensor, bad ignitor, gas supply issue |
| 2 flashes | Pressure switch stuck closed (before inducer starts) | Failed switch, shorted wiring, control board fault |
| 3 flashes | Limit switch open | Overheating, dirty filter, blocked airflow |
| 4 flashes | Limit switch or rollout switch open | Overheating, flame rollout, wiring issue |
| 5 flashes | Gas valve failure or false flame signal | Faulty gas valve, flame sensor misreading |
| 6 flashes | Polarity or ground issue | Reversed hot/neutral, missing or bad ground |
| 7 flashes | Gas valve relay failure | Control board fault, shorted gas valve circuit |
| 8 flashes | Blower motor fault | Failed motor, bad capacitor, ECM module issue |
| 9 flashes | Pressure switch timing error | Inducer not running at speed, blocked vent, failed switch |
Rheem 2-Digit Numeric Code Reference Table
The 2-digit code appears on models with an alphanumeric LED display. These codes provide more specific fault information than the flash count alone.
| Code | Meaning | Diagnostic Direction |
|---|---|---|
| 11 | No previous fault | Normal operation, no stored errors |
| 12 | System in heating mode | Status code, not a fault |
| 13 | Limit circuit lockout | 3 consecutive limit trips, check airflow |
| 14 | Ignition lockout | 3 failed ignition attempts |
| 21 | Gas valve open failure | Gas valve stuck open |
| 22 | Gas valve close failure | Gas valve stuck closed |
| 23 | Gas valve relay short | Control board or wiring fault |
| 24 | Gas valve relay open | Broken wire, open relay |
| 31 | Pressure switch stuck closed | Switch closed when it should be open |
| 32 | Pressure switch stuck open | Switch open when it should be closed |
| 33 | Pressure switch timing | Inducer runs but switch does not close |
| 34 | Auxiliary limit switch open | Secondary limit or rollout switch tripped |
| 41 | Blower motor failure | Motor not running, ECM fault |
| 42 | Blower motor speed error | RPM out of range, bad motor module |
| 43 | Low heat speed error | Specific speed tap issue |
| 44 | High heat speed error | Specific speed tap issue |
| 45 | Blower relay failure | Control board relay fault |
| 51 | Ignitor failure | Open ignitor circuit |
| 52 | Ignitor circuit open | Broken wire, failed ignitor |
| 53 | Flame sensed without call for heat | Stuck gas valve, false flame signal |
| 54 | Flame sensor circuit | Open flame sensor, failed sensor |
| 55 | Combustion air inducer fault | Inducer motor not running |
| 56 | Inducer relay failure | Control board relay fault |
| 57 | Flame sensed with gas valve off | Safety-critical, possible valve leak |
| 58 | Watchdog timeout | Communication or ground fault |
| 61 | Low AC line voltage | Voltage under 103VAC |
| 62 | Polarity fault | Hot/neutral reversed |
| 63 | Ground fault | Missing or high-resistance ground |
| 71 | Auxiliary limit open | Rollout or secondary limit tripped |
Common Code Combinations
Some faults produce both a flash code and a 2-digit code. If you see 3 flashes and code 13, the furnace overheated enough to trip the limit switch. If you see 1 flash and code 14, the furnace tried to light 3 times and failed.
Code 13 (limit circuit lockout) is the most common Rheem service call. A dirty filter causes the furnace to overheat. The limit switch trips. After 3 trips the control board locks out with code 13. Replace the filter and power cycle the furnace.
Code 57 (flame sensed without call for heat) is a safety-critical code. If the gas valve leaks gas past its seat, the flame sensor detects the flame but the control board did not call for heat. The board shuts everything down. This requires professional diagnosis. Do not attempt to reset and ignore code 57.
Rheem Series Differences
Rheem Classic Series (older models): Uses only flash codes. No 2-digit display. The diagnostic LED is amber or green on the control board. Classic models may use a 2-wire or 3-wire pressure switch system.
Rheem Prestige Series: Uses both flash codes and 2-digit numeric display. The control board has a 7-segment LED display that shows the numeric code. Prestige series also has iQ Drive (variable-speed blower) that may show separate blower fault codes.
Rheem Endeavor Series: Current production models. Same dual-code system as Prestige. Endeavor models with EcoNet communicate fault codes to the thermostat. The thermostat may display error text along with the numeric code.
Ruud Achiever, Ultra, and Endeavor: Identical code systems to Rheem. Ruud branding differs but the control boards are the same. Use this guide for any Ruud model.
Diagnostic Workflow
Start with the easiest checks before replacing parts. Most Rheem lockout calls share the same root cause.
- Read the code. Look at the LED flash count and the 2-digit numeric code if available. Write both down before turning power off.
- Power cycle the furnace. Turn the thermostat to OFF. Flip the furnace breaker off for 30 seconds. Restore power and set the thermostat back to HEAT.
- Check the air filter. If the furnace locks out again, check the filter first. A dirty MERV 8 or higher filter on a Rheem furnace will trigger limit lockout (code 13) within one or two heat cycles.
- Inspect the condensate drain. Rheem 90%+ furnaces produce condensate. Blocked drain lines can cause pressure switch lockouts (2 flashes or code 31/32).
- Check the pressure switch tubing. Rubber hoses from the pressure switch to the inducer housing crack and leak over time. Replace any tubing with visible cracks.
- Clean the flame sensor. Remove the flame sensor (one screw, pull vertical). Clean with a fine grit abrasive pad. Reinstall. This resolves most 1-flash or code 14 faults.
- Test the limit switch. Remove the wire connectors from the limit switch. Test continuity with a multimeter. A cold limit switch should read near 0 ohms. Open (infinite resistance) when cold means a failed switch.
When to Call a Professional
Call a technician if the furnace relocks out after you complete the workflow above. Persistent lockout after a clean filter and power cycle points to a component failure (bad pressure switch, failed inducer motor, cracked heat exchanger) that requires specialized tools and gas-safe diagnosis.
Specific situations that require immediate professional attention:
- Code 57 (flame with no call for heat) from any model
- Any rollout switch trip on code 34 or flash code 4
- Gas smell from the furnace or around the gas valve
- Soot or black residue around burner access panels
- Repeated ignition lockout (code 14) after cleaning the flame sensor