Rheem Error Code 12: Rheem Code 12 - Flame Failure
How to Fix Rheem Code 12
- Step 1: Ensure the gas supply to the unit is turned on. Check the shut-off valve on the gas line leading to the water heater.
- Step 2: Reset the unit by turning the power off and then back on. Wait a few minutes to see if the error code clears.
- Step 3: If the error persists after these steps, immediately call a qualified HVAC technician or plumber to inspect the unit. Do not attempt further troubleshooting yourself due to the risk of gas leaks or explosion.
How to Reset Rheem Code 12
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs 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 Rheem Error Code 12 Mean?
Rheem tankless water heaters are designed with multiple safety features. A Code 12, or Flame Failure error, means the unit tried to ignite the burner, but the flame wasn't properly detected or was lost during operation. This is a critical safety issue because unburnt gas can accumulate inside the unit and potentially create a hazardous situation. The system locks out as a safety measure. This error can occur during initial startup, during normal operation, or after a period of inactivity. It's important to address this issue promptly to ensure safe and reliable hot water.
Common Causes
- Gas supply issues (low gas pressure, shut-off valve closed)
- Blocked or partially blocked vent system restricting airflow
- Faulty flame sensor (dirty, mispositioned, or failing)
- Igniter malfunction (weak spark or no spark)
- Defective gas valve (not opening properly)
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Gas supply is suspected | Measure gas pressure at the inlet of the gas valve while the unit attempts to fire | Minimum gas pressure per the unit's specifications (typically 4-7" WC for natural gas, 8-11" WC for propane) |
| Flame sensor is suspected | Measure flame sensor microamp signal during operation | Typically 2-10 uA DC. A reading of 0 uA indicates a problem. |
| Igniter is suspected | Visually inspect the igniter during startup | A strong, consistent spark should be visible. Check igniter resistance (typically 40-100 ohms). |
| Vent blockage is suspected | Visually inspect the vent for obstructions and check vent termination for proper clearance | Clear vent path with proper clearances per installation manual. |
Applicable Rheem Models
- NCB(gas)
- NPE(electric)
- R801T(gas)
- R92E(electric)
- R92V(gas)
- RGE(gas)
- RH2T(electric)
- RNC(dual_fuel)
- RNE(electric)
- RNG(gas)
- RP16(electric)
- RPB(gas)
- RTGH(gas)
- Rheem Classic(gas)
- Rheem Classic 80 Plus(gas)
- Rheem Classic 80% Gas Furnace(gas)
- Rheem Classic 90 Plus(gas)
- Rheem Classic Plus Series(gas)
- Rheem Classic Series(dual_fuel)
- Rheem Prestige(gas)
- Rheem Prestige 95% Gas Furnace(gas)
- Rheem Prestige Series(gas)
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Flame Sensor | — | — | — |
| Gas Valve | — | — | — |
| Igniter | — | — | — |
Related Codes on Same Models
Other codes that affect the same Rheem model families as 12.
| Code | Description | Severity |
|---|---|---|
| A001 | Ignition Failure | Warning |
| A003 | Abnormal Ignition | Warning |
| A004 | False Flame Detection | Warning |
| A008 | Exhaust Temperature High | Warning |
| A011 | No Flame Detected | Warning |
| A021 | Over-Temperature | Warning |
| A031 | Inlet Thermistor Open/Short | Warning |
| A041 | Outlet Thermistor Open/Short | Warning |
| A043 | Water Level Error | Warning |
| A051 | Fan Motor Abnormality | Warning |