Rheem · Water heater
Code 11 Ignition failure (tankless)
What this code means
The unit tried to ignite on startup and failed — the most common tankless water heater fault across every brand.
Most likely causes
- Gas supply valve not fully open or low gas pressure
- Blocked or restricted air intake/vent
- Dirty inlet water filter reducing flow enough to block ignition
What to try first
Confirm the gas shutoff valve at the unit is fully open, and check that the outside vent termination isn't blocked by debris, insects, or snow.
Safety note: if this code returns after one clean reset, stop resetting it — repeated lockouts usually mean a real fault that needs a licensed technician. Never bypass a safety switch.
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What does Rheem error code Code 11 mean?
Ignition failure (tankless). The unit tried to ignite on startup and failed — the most common tankless water heater fault across every brand.
Can I fix Rheem code Code 11 myself?
Usually not. Confirm the gas shutoff valve at the unit is fully open, and check that the outside vent termination isn't blocked by debris, insects, or snow. If the code returns after one reset, it needs a licensed technician.
What causes Rheem code Code 11?
The most common causes are: gas supply valve not fully open or low gas pressure; blocked or restricted air intake/vent; dirty inlet water filter reducing flow enough to block ignition.
Other Rheem water heater codes
All Rheem water heater error codes →
Other water heater brands: Ruud · Rinnai · Navien · Noritz · Takagi · A.O. Smith · Bradford White · State / American · Generic electric · Generic tankless
This information may contain errors or not apply to your exact model — always double-check it against your appliance's own manual before acting. If there's any chance of a gas, fire, electrical, carbon monoxide, or other safety hazard, stop and call a licensed professional or the appropriate agency (e.g. your gas utility) instead of relying on this page alone.