Rheem 11: No Flame Detected

Your Rheem tankless water heater's display is showing 11 and the water isn't heating. This is the single most common fault code on Rheem and Ruud tankless models — it means the unit tried to establish a flame and the flame rod never confirmed one was actually burning.

Applies to: Rheem/Ruud tankless gas water heaters (RTG, RTGH, Prestige series)

What it means

The flame rod does not detect flame when the unit attempts to ignite — the most commonly reported Rheem tankless error. Because the control board treats a no-flame signal as a safety condition rather than a minor glitch, it locks the burner out instead of quietly retrying over and over, which is why the code stays lit on the display until you power-cycle the unit or a technician clears the underlying cause.

Most common causes

Gas supply or inlet pressure issue
Venting problem
Failed igniter rod or flame rod
Gas control valve fault

What you can safely check yourself

Before assuming a part has failed, work through the basics in order:

Verify the gas valve is fully open
Check for any recent changes to venting that could be blocking air flow
Power-cycle the unit

When to call a professional

The code persists after basic gas/power checks — igniter, flame rod, or gas valve testing is needed.

Gas supply lines, gas control valves, and venting should only be worked on by a licensed plumber or HVAC technician. Mains/line-voltage electrical work should be done with the breaker off and, beyond a simple reset, by a qualified electrician or plumber.

What the fix costs

A service call to diagnose a no-flame fault on a Rheem tankless unit typically runs $150–$600 depending on region and what's found, per Angi's and Fixr's water heater repair cost guides. If it turns out to be a failed igniter or flame rod, expect a parts-and-labor repair toward the lower half of that range; a full gas control valve replacement runs closer to $150–$450 installed. Treat these as national ballpark figures rather than a quote — a local licensed plumber can give you an actual number once they've looked at the unit.

Related codes

All Rheem codes

Every Rheem water heater fault code — the full list on one page.

Safety. This code lookup tells you what the control board detected, not that a fix is safe to attempt. If you smell gas, see scorching, or a safety device (thermal fuse, ECO, flammable-vapor sensor) trips more than once, stop and call a licensed professional — do not keep resetting it.

Sources

Rheem/Ruud tankless water heater owner's manual and troubleshooting guide (manufacturer documentation)

This site is an independent reference, not a substitute for a licensed plumber or electrician. Gas water heaters can leak carbon monoxide, leak gas, or catch fire if serviced incorrectly. Anything involving the gas line, gas control valve, venting, or main electrical wiring should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.