Ruud Error Code 12: Flame Failure

Severity
Critical
Type
digital display
Estimated repair cost: $75 — $200 (part only)
Warning: A 'Flame Failure' error indicates a potential gas leak or carbon monoxide risk. Shut down the unit immediately and call a qualified HVAC technician.

How to Fix Ruud Code 12

  1. Step 1: Turn off the furnace immediately at the breaker. This will stop the flow of gas to the unit.
  2. Step 2: Ensure that all vents around the furnace and outside are clear of obstructions like snow, ice, or debris.
  3. Step 3: Check your home's carbon monoxide detectors to ensure they are functioning correctly. Replace batteries if needed.
  4. Step 4: Call a qualified HVAC technician to inspect the furnace and diagnose the root cause of the flame failure.

How to Reset Ruud Code 12

  1. Turn off the furnace power switch, usually located on or near the unit.
  2. Turn off the circuit breaker for the furnace. Wait 30 seconds.
  3. Restore power at the breaker and flip the furnace switch back on.
  4. Set the thermostat to call for heat. If the error code returns after 2-3 ignition attempts, the fault requires repair.

Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.

What Does Ruud Error Code 12 Mean?

The Ruud furnace error code 12, 'Flame Failure,' means the furnace tried to light the burners, but the flame wasn't detected by the flame sensor. This can happen during startup or even while the furnace is running. The control board constantly monitors the flame sensor signal. If the flame isn't sensed when it should be, the furnace shuts down as a safety precaution to prevent unburned gas from accumulating, which could lead to a dangerous situation. This error is critical because it involves gas and combustion. A flame failure can be caused by a variety of issues, ranging from a dirty flame sensor to a problem with the gas valve or even the venting system. Because of the potential safety hazards, it's important to address this issue promptly and correctly.

Common Causes

  • Dirty or faulty flame sensor
  • Gas valve malfunction (not opening or opening intermittently)
  • Ignition failure (failed igniter or spark)
  • Insufficient gas pressure
  • Blocked or restricted flue/venting system
  • Faulty control board

Diagnostic Steps

If... Check Expected
Furnace is locked out on code 12 Measure flame sensor microamps (uA) during burner operation 3-10 uA DC. Low or no reading indicates a problem.
Low flame sensor signal Inspect and clean the flame sensor with steel wool or fine emery cloth Visually clean sensor rod. Retest flame sensor signal.
Flame sensor is clean and signal is still low Check gas pressure at the gas valve with a manometer Natural Gas: 3.5-4.0" WC, Propane: 10-11" WC. Adjust regulator if needed.
Gas pressure is within range Check the resistance of the igniter Typically between 40-90 ohms. Open circuit indicates a failed igniter.

Applicable Ruud Models

Replacement Parts

Part OEM Number Est. Cost Where to Buy
Flame Sensor 47-21501-03 — Find Part
Gas Valve 7000BM1624 — Find Part
Hot Surface Igniter 41-413 — Find Part

Related Codes on Same Models

Other codes that affect the same Ruud model families as 12.

Code Description Severity
11 No Ignition Critical
13 Improper Combustion Critical
14 Overheat / Thermal Fuse Critical
15 Inlet Temp Sensor Fault Warning
16 Outlet Temp Sensor Fault Warning
21 Air Supply / Operational Switch Warning
24 Flow Sensor Malfunction Warning
29 Condensate Neutralizer Issue Warning
31 Inlet Water Filter Warning
33 Fan Motor Fault Warning