Rheem Tankless Gas Code 11
No flame detected. The flame rod does not detect a flame. Rheem's own note on this code is unusually direct about where to look: commonly gas supply and/or venting. Its diagnostic list runs gas supply and venting first, then the igniter rod, the flame rods and the gas control valve — and it reminds the technician to check the altitude DIP switch setting.
Call a proThe verdict
Call a licensed plumber
Confirm gas is reaching the house and the unit; that is the safe part of Rheem's list. Everything else — igniter, flame rods, gas control valve, altitude settings — is inside a sealed gas appliance. Expect a service call, more if a component is replaced.
Typical cost: $150–$900
US estimate for parts and labor. Prices vary by region and by who does the work — see how we estimate costs.
What the manual says
The meaning above is transcribed from the manufacturer's diagnostic documentation for the Tankless Gas — not averaged across the brand.
Source: Rheem Tankless Gas Troubleshooting Pocket Manual (SVC820) (p. 40), read Aug 2026 — the manufacturer's own documentation for this exact series.
What you can safely check
Before anything else: if you smell gas, stop here, leave, and call your gas utility.
- If you smell gas, leave the building and call your gas utility from outside.
- Check that other gas appliances in the house work.
- On propane, check the tank level.
- Confirm the manual gas valve below the unit is open.
- Do not open the front panel to inspect the igniter or flame rods.
Frequently asked questions
Rheem mentions an altitude setting. What has that got to do with ignition?
Air is thinner at altitude, so the same gas flow needs a different air-fuel balance. If the altitude DIP switch was never set for where the unit actually lives, combustion is off from day one — and ignition faults are how that shows up.
How is 11 different from 12?
Code 11 means no flame was ever detected. Code 12 means the unit detected flame and then lost it. Rheem gives both the same headline cause: gas supply and venting.
Don't confuse this with
4 other Rheem Tankless Gas codes point at flame detection too. They are different components in different places, and ordering a part against the wrong one is the most common way this fault gets expensive: