Rheem Tankless Water Heater Code 11 Error
What it means
Code 11 on a Rheem (and the closely related Ruud) gas tankless water heater means 'no ignition' — the unit tried to light the burner but no flame was detected. It applies only to gas-fired models, not electric ones. The usual culprits are a gas-supply problem (valve closed, low pressure, or air in the line) or a dirty/defective igniter, flame sensor, or spark electrode. Most cases trace back to gas delivery or a dirty sensing rod rather than a major part failure. Because it's a gas appliance, only do the external checks yourself and leave internal work to a pro.
Common causes of the Code 11 error
- Manual gas valve to the heater is closed or only partly open
- Low gas pressure or air in the gas line (often after gas service, a new install, or a propane refill)
- Empty propane tank or tripped LP excess-flow valve
- Defective igniter coil — a very common cause of Code 11
- Dirty, misaligned, or sooted spark electrode / flame-sensing rod
- Blocked intake or exhaust venting limiting combustion air
How to fix the Rheem Tankless Water Heater Code 11 error
- 1Make sure the gas is onConfirm the manual gas valve serving the heater is fully open and that other gas appliances in the home work. For propane, check the tank isn't empty and its valve is open. A closed valve or empty LP tank is the most common reason for Code 11.
- 2Power-cycle the unitTurn the heater off for about 30 seconds (use its switch, unplug it, or flip the breaker), then power it back on and run hot water. Code 11 is a lockout, so a reset is required after the cause is fixed.
- 3Clear air from a recently serviced lineIf Code 11 appeared right after gas work, an install, or a propane refill, air may be trapped in the line. Cycling the unit a few times usually lets it draw gas through. If you ever smell gas, stop and call your gas utility or a plumber.
- 4Inspect the ventingCheck the outdoor intake and exhaust terminations for debris, nests, snow, or ice, and make sure airflow is unobstructed. Air is essential to ignition, so a blocked vent can trigger Code 11.
- 5Have a tech check the igniter, electrode, and wiringReseat the front cover and, if comfortable, look for obvious loose or corroded wiring at the ignition and flame rod. If the code persists, the igniter coil, spark electrode, or flame rod likely needs cleaning or replacement — work that involves the gas/burner assembly and should be done by a qualified technician.
🧰 When to call a professional
Call a licensed plumber or Rheem-authorized technician if Code 11 returns after confirming the gas is on and resetting the unit, if you ever smell gas (leave the area and contact your gas utility first), or if the fix requires opening the unit to reach the igniter coil, spark electrode, flame rod, gas valve, or internal wiring. Gas tankless heaters carry gas-leak and carbon-monoxide risks, so combustion and internal repairs should be left to a professional.
Rheem Code 11 error — FAQ
What does Code 11 mean on a Rheem tankless water heater?
Code 11 means 'no ignition' on a gas Rheem (or Ruud) tankless unit — it tried to light the burner but no flame was detected. It's typically caused by a gas-supply issue or a dirty/defective igniter, spark electrode, or flame sensor.
How do I clear Rheem Code 11 myself?
Confirm the gas valve to the heater is fully open and other gas appliances work, then power-cycle the unit off for about 30 seconds and back on, and run hot water. If Code 11 keeps coming back, the igniter, electrode, flame rod, or venting needs a technician.
Why does Rheem Code 11 keep coming back?
A recurring Code 11 usually means an unresolved gas-delivery problem (low pressure, air in the line, empty LP tank) or a failing igniter coil or dirty flame rod. Once the root cause is corrected, the lockout clears after a reset.
Sources
This guide is independently written and not affiliated with Rheem. Always unplug appliances before servicing and follow your model's manual. Error codes and steps can vary by model — when in doubt, consult a qualified technician.