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Rheem Tankless Water Heater Code 11: Ignition Failure Fix

Quick Answer

Rheem Code 11 is an ignition failure. The water heater clicked and attempted to light but the burner never established a flame. The most common cause is a dirty flame rod (also called a flame sensor or flame detector) that cannot detect the burner flame even when ignition fires.

Rheem Code 11 is an ignition failure. The water heater clicked and attempted to light but the burner never established a flame. The most common cause is a dirty flame rod (also called a flame sensor or flame detector) that cannot detect the burner flame even when ignition fires. Cleaning the flame rod with fine steel wool or emery cloth resolves Code 11 in roughly 45% of cases. Other causes: gas supply valve partially closed, low gas pressure, igniter electrode gap worn, or gas valve fault. Always verify gas is on before beginning diagnosis.

RheemWaterheaterSeverity: highDifficulty: intermediate70% DIY Success
Time to Fix
20–90 min
Difficulty
intermediate
Parts Cost
$15 – $50
Tools Needed
Phillips screwdriver, 400-grit emery cloth or fine steel wool
Wrong code?

Not seeing 11 on your display?

Select what your appliance is actually doing and we'll take you to the right guide.

ignition failure
Rinnai11
ignition failure
Noritz11

What Does the 11 Code Mean?

Rheem Code 11 means ignition failed. Check that gas is on, then clean the flame rod with fine steel wool. If that does not fix it, test igniter electrode gap and gas valve.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Dirty or oxidized flame rod unable to sense the burner flame40%
Gas supply valve closed, low gas pressure, or gas service interrupted24%
Gas valve solenoid fault preventing gas flow to burner22%
Worn or damaged igniter electrode failing to produce spark14%

Symptoms You May Notice

  • Code 11 displayed on LCD
  • Clicking sounds during startup followed by shutdown
  • No hot water output
  • Unit powers on but does not produce heat
  • Repeated ignition attempts before lockout

Can you reset a Rheem waterheater to clear the 11 code?

Unplug the appliance for 60 seconds, then reconnect power to clear stored error codes.

Tools Required for Diagnosis

Phillips screwdriver400-grit emery cloth or fine steel woolMultimeter (to test flame rod continuity)

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

1

Verify the gas supply

Verify the gas supply: check that the gas shutoff valve on the supply line to the water heater is fully open (handle parallel to pipe). On propane systems, check tank level. Try running another gas ap

2

Reset the unit by pressing the Reset button or holding Power for

3

Turn off the gas supply

4

Disconnect the flame rod wire

5

Restore gas supply, replace the access panel, and test

Replacement Parts

If your diagnostic testing proves the component has failed, you will need a replacement. We recommend OEM parts over aftermarket for water-handling components.

Part Name
Rheem flame rod / flame sensorAP15516-1 · $15–$35
Rheem igniter electrode assemblyAP15517-1 · $20–$50

Repair vs. Replace Calculator

Appliance Age (Years)7 Yrs
Labor Approach
Our Verdict
REPAIR
Estimated Cost: $33 (Parts) vs $1050 (New Machine)

Frequently Asked Questions

How long does it take to clean the flame rod on a Rheem tankless water heater?
Cleaning the flame rod takes about 15-20 minutes including panel removal and reinstallation. The cleaning itself takes under 5 minutes. It is one of the most effective DIY repairs for Code 11 with no special tools required beyond a screwdriver.
Why does the flame rod cause Code 11 if the burner actually lit?
The flame rod works by passing a small electrical current through the flame. An oxidized or carbon-coated rod has high resistance and cannot pass enough current to convince the control board that ignition succeeded, even when a flame is present. The board shuts down as a precaution.
How often should I clean the Rheem flame rod?
Annual cleaning of the flame rod is good preventive maintenance on any tankless water heater. Units that sit unused for months (vacation homes, seasonal properties) should be cleaned before seasonal start-up.
My Rheem still shows Code 11 after cleaning the flame rod. What next?
If Code 11 persists after flame rod cleaning, check the igniter electrode for wear, cracks, or carbon deposits. The electrode gap should be 3-4mm. Also check gas pressure at the inlet with a manometer: natural gas should be 4-11 inches WC, propane 8-14 inches WC. If pressure and ignition are confirmed good, the gas valve may have a stuck solenoid.
Is Rheem Code 11 the same as Rinnai Code 11?
Both codes indicate ignition failure and the diagnostic steps are similar. The specific component locations and cleaning procedures differ by brand. The flame rod cleaning fix applies to both, but part numbers and access procedures are brand-specific.

Related Rheem Waterheater Error Codes

Code: HUBRheem Tankless Water Heater Error Codes: Performance Plus and Prestige Series Guide

Same Fix on Other Brands

Rinnai waterheater11: Rinnai Code 11: No IgnitionNoritz waterheater11: Noritz Code 11: No Ignition

Models Known to Experience 11 Errors

This repair applies to most Rheem waterheaters with this error code. Common model numbers include:

RTGH-95DVLN, RTGH-84DVLN, RTG-95XLN

Last verified for technical accuracy on March 14, 2026