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Seeing Rheem tankless water heater code 11 or another code? Rheem gas units show numeric codes on the controller, and electric models use their own codes. Here’s how to read them.
Code 11 on a Rheem gas tankless water heater means ignition failed. Work through these checks:
The burner lit but the flame was lost. Check the vent and intake terminals for blockages and look for wind exposure. Low gas pressure, often caused by an undersized gas line when other appliances run, is a frequent cause. A dirty flame sensor can also trigger code 12.
Rheem tankless water heater code 12 that returns repeatedly needs a technician.
| Code | Commonly indicates | First step |
|---|---|---|
| 10 | Air supply or exhaust blockage (many gas models) | Inspect vent and intake terminals |
| 11 | No ignition | Gas supply and pressure |
| 12 | Flame failure | Gas pressure and venting |
| LC | Scale buildup (models with scale detection) | Flush the unit |
| 13, 17, 29 and others | Model-specific faults | Check the chart for your model |
| P1, E5 and other letter codes | Model-specific, often on electric or newer models | Check the chart for your model |
Rheem has changed code tables between generations and between gas and electric lines, so always confirm with the manual for your model number. Rheem publishes manuals on its website, and many units have a code chart inside the front cover.
Rheem electric tankless water heaters (such as the RTEX series) use their own diagnostic codes, often related to temperature sensors, flow, or elements. Before troubleshooting an electric unit, turn off all breakers that feed it. Tripped breakers, failed heating elements and scaled elements are common issues.
Call a licensed technician or a Rheem-authorized service provider if a code returns after basic checks, if you smell gas, or if the code involves combustion, overheating, the fan or control board. For more help, see tankless water heater repair and troubleshooting and our Rheem tankless guide.
Yearly flushing keeps Rheem units running cleanly.
No ignition. The unit tried to light but didn’t detect a flame. Check that the gas valve is open, the propane tank has fuel, and other gas appliances work. Persistent code 11 needs a technician to check gas pressure, the igniter and the flame sensor.
Flame failure, meaning the flame went out during operation. Common causes are low gas pressure, a blocked vent or air intake, or a dirty flame sensor.
These codes are model-specific. Some relate to condensate, pressure or electrical faults depending on the model and whether it is gas or electric. Check the chart inside the front cover or the manual for your model number before taking action.
Fix the cause, then turn the unit off and on using the controller or by cycling power. If the code returns, contact a Rheem-authorized service provider.
This guide is general information for U.S. homeowners, not professional advice. Gas, electrical and venting work must follow the manufacturer’s instructions and local codes, and in most areas requires a licensed plumber, electrician or gas fitter and a permit. Specifications and prices change; always confirm details on the product page and in the installation manual.
