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Rheem code 11 (flame not detected): what to check

By How House Works EditorialBased on Rheem manualsChecked against sources Updated

Rheem display

11

“The gas shut-off valve is not fully opened.”

RTGH-3, RTG-3, RTG-R-3, Ruud Mid-Efficiency · RTGH-3 Use and Care Manual, p. 75; RTG-3 Use and Care Manual, p. 77; RTG-R-3 Use and Care Manual, p. 74; RTGH-3 and RTG-3 Troubleshooting Manual, p. 37; RTG-R-3 Troubleshooting Manual, p. 30; Tankless Water Heater Use and Care Manual AP18000-2, p. 26
Owner checks, then technician

Troubleshooting manual name: "Flame Not Detected by Flame Rod". The heater attempts ignition 2 times before it shows 11 (AP21822 tech manual, p. 37).

What it means

Code 11 means the burner did not light. After an ignition failure the heater tries to light 2 times, and if its flame rod still detects no flame, it shows 11 RTGH-3 and RTG-3 Troubleshooting Manual, AP21822, p. 37; RTG-R-3 Troubleshooting Manual, AP24838, p. 30. The owner charts give one cause and one remedy: check the gas shut-off valve and open it completely RTGH-3 Use and Care Manual, p. 75; RTG-3 Use and Care Manual, p. 77; RTG-R-3 Use and Care Manual, p. 74.

These heaters have no pilot. An ignition device lights the burner, and the label says not to try lighting it by hand RTGH-3 manual, p. 6.

Check these first

If a gas leak is present or suspected, do not try to find the cause yourself RTGH-3 manual, p. 5.

  1. Close all hot water taps. Turn the heater off with the POWER ON/OFF button on the remote control, wait about 5 minutes, turn it back on, then open a hot tap and check the display RTGH-3 manual, p. 74; RTG-3 manual, p. 76; RTG-R-3 manual, p. 73.
  2. If 11 is still shown, close the tap, turn the heater off, unplug it for about 30 seconds and plug it back in RTGH-3 manual, p. 74.
  3. Check that the gas shut-off valve is fully open RTGH-3 manual, p. 75. The label’s operating instructions place this valve on the outside of the unit; it turns counterclockwise to ON RTGH-3 manual, p. 6. Rheem says not to turn the heater on unless the gas and water supplies are completely open RTGH-3 manual, p. 5.
  4. If the valve was closed, reopen it the way the label describes: turn off electric power to the heater, set the valve to OFF and wait five minutes. Then smell for gas around the heater, including next to the floor. If you smell gas, stop and follow the gas steps above. If you do not, turn the valve to ON and turn the power back on RTGH-3 manual, p. 6.
  5. Restart the heater, open a hot tap and check the display. If 11 is still shown, turn the heater off, write down the code and call for service RTGH-3 manual, p. 74. The label adds that if the heater will not operate, you turn off the gas to it and call your service technician or gas supplier RTGH-3 manual, p. 6.

When to call a licensed technician

  • Code 11 comes back after the valve check and the reset.
  • Anything on the troubleshooting manual’s list for 11. Rheem writes that manual for technicians and service professionals only AP21822 tech manual, p. 7. Its checks are the gas supply pressure at the heater’s gas connection, measured at standby and at maximum firing; the gas filter at that connection; the vent connections and termination; DIP switch settings for venting and altitude; and the igniter and flame rods AP21822 tech manual, p. 37.
  • The pressure window the technician checks against is 4.0–10.5 in. w.c. for natural gas and 8.0–13.0 in. w.c. for propane AP21822 tech manual, p. 37; RTGH-3 manual, p. 5. If the pressure is too high or too low, the Use and Care manual says to contact your gas supplier for correction RTGH-3 manual, p. 45.
  • The charts do not link 11 to gas line size. The RTGH-3 manual does say that an undersized flexible gas connector will cause operational issues, and that half-inch gas lines are permitted only when the system pressure is 8.0 in. w.c. or more and the pipe capacity table is followed RTGH-3 manual, p. 43. Gas piping is not an owner repair RTGH-3 manual, p. 5.
  • Above 2,000 ft (610 m), a qualified service technician makes the altitude adjustments RTGH-3 manual, p. 47.

Notes for different models

The RTGH-3, RTG-3 and RTG-R-3 charts print the same row for 11, and so does the chart for Ruud Tankless Mid-Efficiency heaters Tankless Water Heater Use and Care Manual AP18000-2, p. 26.

IKONIC heaters show A011 for the same cause. Their chart also asks you to check that venting and the air supply are not blocked IKONIC Use and Care Manual, p. 107, and the service manual says the heater makes 10 ignition attempts before it shows A011 IKONIC Technical Training and Service Manual, p. 38.

Related Rheem codes

  • 12 “Gas service has been interrupted.”
  • 72 “Flame rod detected flame before ignition”
  • 90 “Air intake or vent exhaust opening may be blocked.”

All Rheem codes

Rheem is a trademark of its owner. How House Works is not affiliated with or endorsed by Rheem.

Sources

  1. Rheem Manufacturing Company. RTGH-3 Use and Care Manual. AP21820 Rev 06, no printed date; cover title: Super High Efficiency Condensing Tankless Water Heater Use and Care Manual; the same file is posted for Ruud RUTGH models; p. 1 is the unnumbered cover. Accessed Oct 12, 2026.
  2. Rheem Manufacturing Company. RTG-3 Use and Care Manual. AP22009 Rev 06, no printed date; cover title: High-Efficiency Non-Condensing Tankless Water Heater Use and Care Manual; the same file is posted for Ruud RUTG models. Accessed Oct 12, 2026.
  3. Rheem Manufacturing Company. RTG-R-3 Use and Care Manual. AP23962 Rev 02, no printed date; cover title: High-Efficiency Non-Condensing Tankless Water Heater with Recirculation Use and Care Manual; the same file is posted for Ruud RUTG-R models. Accessed Oct 12, 2026.
  4. Rheem Manufacturing Company. RTGH-3 and RTG-3 Troubleshooting Manual. AP21822 Rev 02, no issue date printed; cover title: High and Super High Efficiency Tankless Water Heater Troubleshooting Manual; written for technicians and service professionals only (p. 7). Accessed Oct 12, 2026.
  5. Rheem Manufacturing Company. RTG-R-3 Troubleshooting Manual. AP24838 Rev 01, no issue date printed; cover title: High Efficiency Tankless Water Heater with Recirculation Troubleshooting Manual; written for technicians and service professionals only (p. 6). Accessed Oct 12, 2026.
  6. Rheem Manufacturing Company. IKONIC Use and Care Manual. AP22745 Rev 07, no printed date; cover title: Condensing Tankless Water Heater Use and Care Manual; Ruud's S and SR Series pages post Rev 06. Accessed Oct 12, 2026.
  7. Rheem Manufacturing Company. IKONIC Technical Training and Service Manual. AP23209 Rev 03, no printed date; written for technicians and service professionals only (p. 4). Accessed Oct 12, 2026.
  8. Rheem Manufacturing Company (posted on ruud.com). Tankless Water Heater Use and Care Manual AP18000-2. AP18000-2 Rev 03, no printed date; cover title: Tankless Water Heater Use and Care Manual, Noncondensing 199,900 Btu/h, 180,000 Btu/h, and 150,000 Btu/h Models; the manual prints no model numbers and no -3 suffix; ruud.com posts it on its Tankless Mid-Efficiency 70, 84 and 95 product pages (2026-10-12). Accessed Oct 12, 2026.