Rheem error code 11 = ignition failure. The unit attempted to light the burner three times and detected no flame. In most cases the fix takes under 20 minutes: check the gas supply valve is open, then clean the flame sensor rod with fine steel wool. If the code persists after both steps, work through the full checklist below.
What Does Rheem Error Code 11 Mean?
On all Rheem tankless water heater models — including the RTG-84, RTGH-95, and Performance Plus series — error code 11 is an ignition failure lockout.
When you open a hot-water tap, the unit tries to ignite the burner up to three times. If the flame sensor rod does not detect a stable flame within the allotted time, the control board shuts everything down and displays code 11 as a safety measure.
The unit is not damaged. It is locked out waiting for you to identify and fix the root cause, then perform a reset.
Rheem RTG/RTGH series — code 11 displays on the front LED panel
Rheem code quick reference
Ignition failure
This guide
Flame loss during operation
Related
Combustion air failure
Related
6 Common Causes of Rheem Code 11
Work through these in order — the first two resolve about 70% of code 11 cases.
Gas supply or pressure issue
The burner can't light without adequate gas. A closed shutoff valve, low line pressure (under 3.5" WC for natural gas), or an upstream supply interruption are instant code 11 triggers.
Dirty or corroded flame sensor rod
The sensor rod detects the flame via electrical conductivity. Oxidation on the rod tip insulates it, making the unit 'think' ignition never happened even when it did.
Blocked air intake or exhaust vent
Debris, ice, bird nests, or an improperly pitched vent pipe can starve the burner of combustion air or create back-pressure that prevents ignition.
Clogged inlet water filter screen
A partially blocked cold-water inlet screen reduces flow below the minimum activation threshold (usually 0.5 GPM), preventing the unit from firing at all.
Water flow rate too low
Rheem tankless units require a minimum flow to activate the burner. A partially closed fixture, a low-flow aerator, or sharing load with other appliances can drop flow below the trigger point.
Faulty igniter or gas valve
If all DIY checks pass but code 11 persists, the igniter may be cracked, the gas valve solenoid may have failed, or the control board may be sending incorrect signals.
Step-by-Step: How to Fix Rheem Code 11
Total time: 20–30 minutes for a DIY fix. Tools needed: flat-head screwdriver, fine steel wool, flashlight.
Check the gas supply valve
schedule2 minFind the gas shutoff valve on the pipe leading directly to your water heater. The handle must be parallel to the pipe — not perpendicular (off). Also light a gas burner on your stove or furnace to confirm the main supply is live.
Reset the unit
schedule2 minPress the Reset button on the front panel (some models require holding it 3 seconds). Or switch the circuit breaker OFF, wait 30 seconds, and switch it back ON. Let the unit complete its startup sequence before calling for hot water.
Clean the flame sensor rod
schedule10–15 minTurn off gas and power. Locate the flame sensor rod — a metal rod with a ceramic insulator near the burner assembly. Gently rub the tip with fine steel wool or emery cloth to remove oxidation (don't over-sand). Reinstall, restore power, and test.
Clean the inlet water filter screen
schedule5–8 minClose the cold-water inlet valve. Unscrew the cold-water inlet fitting and pull out the small mesh filter screen. Rinse it under the tap to clear mineral deposits or sediment. Reinstall, re-open the valve, and test.
Inspect the venting system
schedule5 minGo outside and visually inspect both the exhaust outlet and the air intake terminal. Look for debris, snow/ice, insect nests, or crushed duct sections. Verify the vent pipes slope correctly (check your model's installation manual for required pitch).
Verify minimum water flow
schedule2 minOpen two hot-water fixtures at the same time (a shower + a sink, for example) to increase total flow above the 0.5 GPM activation threshold. If the unit fires with more flow but not less, you need to address low-flow fixtures or check the inlet valve.
Still showing code 11? Call a professional
schedule—If all six checks above pass and code 11 persists, the fault is likely inside the unit: a cracked igniter electrode, a failed gas valve solenoid, or a control board issue. These require a multimeter, gas-pressure gauge, and a licensed technician.
Video Walkthrough: Fixing Rheem Code 11
Prefer to watch? This step-by-step video covers the most common ignition failure fixes for Rheem tankless water heaters.
"How to Fix Rheem Tankless Water Heater Code 11 – Step by Step Ignition Fix Guide"
Rheem Models Affected by Code 11
Error code 11 appears on all current Rheem tankless water heater lines. The diagnosis steps in this guide apply to every model listed below.
- checkRTG-64DVLN / RTG-64DVLP
- checkRTG-84DVLN / RTG-84DVLP
- checkRTGH-84DVLN / RTGH-84DVLP
- checkRTGH-95DVLN / RTGH-95DVLP
- checkRTG-84DVLN-2 (and variants)
- checkPerformance Series (NG & LP)
- checkPerformance Plus Series
- checkEcosense RTE Series
When to stop and call a professional
- arrow_rightYou smell gas at any point — evacuate and call your gas utility immediately
- arrow_rightCode 11 persists after completing all six steps in this guide
- arrow_rightThe unit is under warranty — DIY repairs beyond cleaning may void it
- arrow_rightYou are not comfortable working around gas appliances
Frequently Asked Questions
- How do I reset Rheem error code 11? expand_more
- Press the Reset button on the unit's front panel. Alternatively, switch the circuit breaker off, wait 30 seconds, then switch it back on. If code 11 returns immediately, an underlying cause still needs to be addressed.
- What is the most common cause of Rheem code 11? expand_more
- A dirty or oxidized flame sensor rod is the single most common culprit. The oxidation prevents the rod from detecting the flame signal, even when ignition briefly succeeds. A quick clean with fine steel wool usually resolves it.
- Can I fix Rheem error code 11 myself? expand_more
- Yes — in most cases. Checking the gas valve, cleaning the flame sensor rod, and clearing the water filter are all safe DIY steps. If the igniter or gas valve is faulty, a licensed technician should handle the repair.
- Why does Rheem code 11 come back after a reset? expand_more
- A recurring code 11 after reset means the root cause hasn't been fixed. The most common repeat offenders are a dirty flame sensor rod, low gas pressure, or a partially blocked vent.
- Does error code 11 damage my Rheem water heater? expand_more
- No. Code 11 is a safety lockout — the unit shut down before any damage could occur. Resolving the ignition issue and resetting is all you need.
- What is the difference between Rheem code 11 and code 13? expand_more
- Code 11 = ignition failure (flame not established). Code 13 = combustion air supply problem (blocked intake or downdraft). Both affect ignition but from different subsystems — diagnosis steps differ.
Pro tip
Take a photo of your water heater's rating plate before your service call. The model and serial number speed up parts ordering by 30+ minutes.