Rheem Tankless Water Heater Flame Sensor Replacement Guide — What This Part Does
The flame rod (flame sensor) proves that combustion is established during ignition and monitors it continuously while the burner runs. It sends a signal to the control board confirming flame presence so gas flow can continue safely. The sensor sits in the flame path and uses flame rectification to detect ionized combustion gases.
The sensor fails or gives false readings when carbon deposits coat the rod, when the connector or wiring degrades, or when the rod becomes corroded or physically damaged. Dirty sensors are the most common issue. Low gas pressure, blocked venting, or contaminated combustion air can also cause the sensor to report intermittent or no flame even when ignition occurs.
Signs It Needs Replacing
- Unit displays flame proving or flame detection fault code The control board shows an error indicating it cannot confirm flame presence during or after ignition.
- Heater ignites then shuts off within seconds The burner lights but the unit locks out immediately because the sensor does not detect flame.
- No ignition at all despite clicking or spark The igniter fires but the unit will not open the gas valve or sustain gas flow because flame is not proven.
- Visible carbon buildup or discoloration on the flame rod The rod tip is coated with black soot or shows heavy oxidation when inspected inside the burner chamber.
- Intermittent operation or random shutdowns The heater runs normally sometimes but trips flame faults unpredictably during use.
- Fault code indicating flame detected before ignition The board reports flame signal present when no ignition command was given, pointing to a shorted or failing sensor.
How to Replace It
- Turn off electrical power to the water heater at the circuit breaker or disconnect switch.
- Close the gas supply valve to the unit completely.
- Close the cold water inlet valve and relieve pressure by opening a hot water tap downstream.
- Remove the front cover or access panel to expose the burner chamber and flame sensor assembly.
- Locate the flame rod, which is a thin metallic rod positioned near or in the burner flame path, and disconnect the wire connector at its base.
- Unscrew the mounting bracket or retaining fastener securing the flame rod to the burner assembly or chassis and carefully pull the rod out.
- Install the new flame sensor in the same position and orientation, tighten the mounting fastener snugly, and reconnect the wire connector firmly.
- Reinstall the access panel, open the cold water valve, restore gas supply, and restore electrical power.
- Run a hot water tap to purge air, then monitor the unit through a full heating cycle to confirm normal ignition and flame proving without fault codes.
The Part You Need
| Part | Notes |
|---|---|
| Rheem Flame Rod / Flame Sensor Assembly | Amazon | Find your exact part number on the model and serial plate located on the front or side of the tankless heater. Match the sensor design and connector type to your specific Rheem model. |
Related Error Codes
If this part is failing you may also see one of these codes:
When to Call a Pro
If you still see flame proving faults after cleaning or replacing the sensor, the problem is likely gas pressure (incoming supply should be 5.0 to 13.0 inches water column or 1.25 to 3.24 kPa), venting blockage, gas valve failure, or control board issues. Any work involving gas valve replacement, igniter testing, burner removal, or combustion diagnostics should be handled by a licensed gas technician. If you are uncomfortable working around gas lines or live electrical components, call a qualified service professional before opening the unit. For gas line, burner, or igniter work, or if you ever smell gas, stop and call a licensed technician.