Rheem Tankless Gas Code 80
Gas control valve: flame detected after shutdown. The unit detected the presence of flame when the demand for hot water ended and it had turned off — the same explanation Rheem gives for code 51, pointing at the gas control valve.
Call a proThe verdict
Call a licensed plumber
Treat it exactly like code 51: gas may still be reaching the burner with the unit off. Close the manual gas valve and get it looked at before using it again.
Typical cost: $400–$1,100
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. 89), 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.
- Turn the heater off and close the manual gas valve below it.
- If you smell gas, leave the building and call your gas utility from outside.
- Book a licensed professional promptly.
Frequently asked questions
Why do codes 51 and 80 have the same explanation?
Rheem gives both the same wording and the same first diagnostic — the flame rod and the gas control valve. They are separate code numbers for the same condition detected at different points, and neither is one to ignore.
Don't confuse this with
5 other Rheem Tankless Gas codes point at a valve 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: