12
Rheem Water Heater
Severity: ModerateWhat Does This Error Mean?
Error 12 means the burner lit but the flame went out unexpectedly during operation. Common causes are low gas pressure, a dirty flame sensor, blocked combustion air, or wind affecting the vent.
Affected Models
- Rheem Performance Tankless
- Rheem Performance Plus Tankless
- Rheem Prestige Tankless
- Rheem Gas Water Heater
Common Causes
- Low gas pressure (small propane tank, partially closed valve, undersized supply line)
- Dirty flame sensor unable to detect a steady flame
- Wind blowing flame out of position at vent termination
- Restricted combustion air supply
- Faulty gas valve cycling on and off
How to Fix It
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Reset the unit and observe.
Turn off power at the breaker for 30 seconds. Reset and observe whether Error 12 reappears immediately or after some operation. Immediate failure indicates a sensor or pressure issue; later failure points to wind or vent problems.
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Check the gas supply pressure.
Verify the gas shutoff valve is fully open. LP propane tanks below 25% can deliver inadequate pressure. Refill or replace small propane tanks. Natural gas pressure issues require a licensed technician.
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Inspect the vent termination.
Look at where the vent exits outside. Wind, snow blowing into the vent, or improper termination near a corner can disrupt the flame. A vent terminator hood often resolves wind-related flame loss.
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Clean the flame sensor.
This requires a licensed technician. The flame sensor (a thin metal rod inside the burner chamber) accumulates oxide and stops detecting flame. Cleaning with a fine emery cloth restores function.
When to Call a Professional
Persistent Error 12 after basic troubleshooting indicates a gas pressure or component issue. A licensed plumber or gas technician can measure inlet pressure and test the flame sensor.