Ruud Furnace Code 57 typically notifies the homeowner or technician that the furnace control board detected a problem during the ignition or flame sensing sequence. This article explains what Code 57 means, the most common causes, step-by-step troubleshooting, parts and typical repair costs, and preventive maintenance to reduce recurrence. The guidance is written for U.S. residential users and emphasizes safety and when professional service is recommended.
| Item | Summary |
|---|---|
| Typical Meaning | Ignition failure or abnormal flame sensing during the start cycle |
| Common Causes | Dirty flame sensor, faulty flame sensor, ignition failure, blocked venting, pressure switch or inducer issues, gas supply or valve problem, control board fault |
| Initial Checks | Reset furnace, check thermostat and power, inspect gas supply, look for error LED flashes on control board |
| When To Call A Pro | Any gas-related component, repeated failures after basic cleaning, if not comfortable working with gas/electrical parts |
What Code 57 Means On A Ruud Furnace
Code 57 on many Ruud furnaces is a diagnostic indicator from the control board that the unit failed to detect a proper flame during the ignition sequence or experienced an irregular flame signal. The board aborts the start cycle to protect the system when flame confirmation does not occur as expected.
Key Point: Code 57 is a safety response; it prevents sustained gas flow without verified combustion and reduces risk of unburned gas or unsafe operation.
How The Furnace Ignition Sequence Works
Understanding the ignition sequence helps make sense of Code 57. Typical steps include: the thermostat calls for heat, the control board powers the inducer/vent motor, the pressure switch confirms airflow, the ignitor or pilot lights, the gas valve opens, and the flame sensor confirms flame presence.
If any step fails or if the flame sensor does not register a stable flame, the board will shut down the attempt and log an error such as Code 57.
Common Causes Of Code 57
Dirty Or Faulty Flame Sensor
A flame sensor coated with carbon or oxidation is the most frequent cause of flame-detection errors. A dirty sensor may not produce the small steady electrical signal the board expects.
Ignitor Problems
A cracked or failing hot surface ignitor will not reliably ignite the gas. If the ignitor glows but flame does not establish, the system may log Code 57.
Gas Supply Or Gas Valve Issues
If there is insufficient gas pressure, a blocked gas line, or a malfunctioning gas valve, the burner will not light properly and the flame sensor will not detect combustion.
Inducer Motor or Pressure Switch Faults
A failing inducer motor or a stuck/defective pressure switch can prevent proper venting verification. The control board may either stop the start sequence or allow ignition without proper vent confirmation, triggering an error.
Blocked Venting Or Flue Problems
Restricted exhaust or intake can disrupt combustion air flow. The system may fail to stabilize a flame, which can lead to Code 57 or other ignition-related codes.
Control Board Or Wiring Faults
Damaged wiring, loose connections, or a defective control board can produce false flame signals or fail to interpret the flame sensor correctly.
Step-By-Step Troubleshooting Guide
Safety First
Before any inspection: shut off power to the furnace at the service switch and the breaker. If gas smells are present, evacuate the area and call the gas company or emergency services. Do not attempt repairs if uncomfortable working with gas or electrical components.
1. Check Thermostat And Power
Confirm the thermostat is set to heat and above room temperature. Ensure the furnace has 120V power and the service switch is on. A simple power interruption can display stored codes.
2. Clear And Reset
Many Ruud units allow a reset by switching power off for 30 seconds then on. If Code 57 persists after a reset and another call for heat, proceed to inspection steps.
3. Inspect The Flame Sensor
Locate the flame sensor (thin metal rod near the burner). Remove it and gently clean with fine-grit sandpaper or emery cloth to remove carbon buildup. Reinstall and retest.
Why This Works: Cleaning restores the micro-current path needed for the control to sense flame.
4. Check The Ignitor
Visually inspect the hot surface ignitor for cracks or damage. A glowing but unstable or intermittently failing ignitor can cause no-flame conditions. Replace the ignitor if any damage is observed.
5. Verify Gas Supply
Ensure other gas appliances operate to confirm supply. If the furnace smells of gas during an attempted ignition, stop and call a qualified technician. A licensed pro should test manifold pressure and gas valve function.
6. Examine Inducer And Pressure Switch
Check the inducer motor for operation during startup. Inspect the pressure switch hose for cracks or blockages and confirm the switch closes when the inducer runs. Replace obstructed tubing and test the pressure switch continuity if skilled in electrical testing.
7. Inspect Venting And Air Intake
Look for obstructions at the intake and exhaust terminations (birds’ nests, debris, snow). Clear any blockage and ensure proper sealing and routing of vent pipes.
8. Check Wiring And Grounding
Examine wiring to the flame sensor, ignitor, gas valve, and control board for loose connections, corrosion, or damaged insulation. A poor ground or bad connector can cause false readings.
9. Observe Error Codes And LED Flash Patterns
Many Ruud control boards indicate specific errors through LED blink counts. Consult the furnace service manual or the data plate for the LED code chart to confirm whether Code 57 aligns with the observed blinks.
When Replacement Is Likely Required
If cleaning the flame sensor and replacing a failed ignitor do not resolve Code 57, the gas valve, pressure switch, inducer motor, or control board may be failing. Professional diagnosis with multimeter readings and pressure tests is recommended for these components.
Typical Replacement Candidates: flame sensor, hot surface ignitor, pressure switch, inducer motor, gas valve, control board.
Typical Repair Costs And Parts
Costs vary by region and furnace model. Below are ballpark ranges to help plan.
| Part/Service | Estimated Cost Range (Parts + Labor) |
|---|---|
| Flame Sensor Cleaning/Reinstall | $0–$75 (if homeowner cleans) / $75–$150 (tech labor) |
| Flame Sensor Replacement | $40–$120 (part) + $75–$200 (labor) |
| Hot Surface Ignitor | $40–$150 (part) + $100–$250 (labor) |
| Pressure Switch | $40–$150 (part) + $100–$250 (labor) |
| Inducer Motor | $150–$450 (part) + $150–$400 (labor) |
| Gas Valve | $150–$400 (part) + $150–$400 (labor) |
| Control Board | $150–$600 (part) + $150–$400 (labor) |
When To Call A Professional HVAC Technician
Call a licensed HVAC technician if any gas-related component needs diagnosis or replacement, if the homeowner is not trained in electrical testing, if repeated Code 57 events occur, or if a reset does not clear the fault after basic cleaning.
Safety Reminder: Working on gas valves, manifold pressure, or sealed combustion systems requires specific training and licensing.
Preventive Maintenance To Reduce Future Code 57 Events
- Schedule annual professional furnace maintenance before the heating season.
- Have the flame sensor inspected and cleaned during service visits.
- Replace air filters regularly to maintain proper airflow.
- Keep intake and exhaust terminations clear of debris and snow.
- Ensure proper combustion air by keeping surrounding areas clear and vents unobstructed.
How To Document The Problem For A Technician
When contacting a technician, provide: the model and serial number from the furnace data plate, the exact error code displayed (Code 57), any observed LED blink pattern, what troubleshooting steps were taken, and when the issue began. This information speeds diagnosis and helps the technician bring the right parts.
Additional Resources And Manufacturer Support
Ruud owner manuals and technical bulletins provide model-specific LED code charts and wiring diagrams. The model data plate and the service manual are the best reference for exact meanings of error codes. For warranty or OEM parts information, contact Ruud customer support or an authorized dealer.
Ruud Official Site can direct users to manuals, service locator tools, and customer support contacts.
Key Takeaways And Best Practices
Code 57 Indicates A Flame-Related Ignition Issue: It commonly relates to flame sensing, ignition failure, gas supply, or airflow/venting problems.
Start With Simple Checks: reset power, confirm thermostat and power, clean the flame sensor, inspect the ignitor and vents.
Call A Professional For Gas Or Complex Electrical Issues: technicians can safely test gas pressures, verify inducer and pressure switch operation, and diagnose control board faults.