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Rheem code 99 (vent blockage after shutdown): what to check

By How House Works EditorialBased on Rheem manualsChecked against sources Updated

Rheem display

99

“Air intake or vent exhaust opening may be blocked.”

RTGH-3, RTG-3, RTG-R-3 · 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. 61; RTG-R-3 Troubleshooting Manual, p. 56
Owner checks, then technician

Same chart row as 90 ("90 or 99"). The troubleshooting manual says 99 occurs after the unit shuts down and lists it with 10 and 13 as a "hard lockout" whose reset starts with removing the front cover (AP21822 tech manual, p. 61). Ruud Tankless Mid-Efficiency heaters use 99 for something else: their chart prints "61 or 99" as "Faulty blower motor.", with a call to a dealer or qualified service technician (AP18000-2 manual, p. 26).

What it means

Code 99 is the after-shutdown version of 90. Rheem’s troubleshooting manual says the heater checks for a blockage in the venting during its pre-purge and post-purge cycles, and that 99 occurs after the unit shuts down, while 90 occurs before ignition RTGH-3 and RTG-3 Troubleshooting Manual, AP21822, p. 61; RTG-R-3 Troubleshooting Manual, AP24838, p. 56. In the owner charts, 90 and 99 share one row: the owner clears a blocked air intake or vent exhaust opening, and vent pipes not connected properly at the termination go to a dealer or qualified service technician 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.

The troubleshooting manual also lists 99, with 10 and 13, as a “hard lockout”. Its reset procedure starts with turning the remote off, removing the front cover and setting DIP switches on the control board AP21822 tech manual, p. 61. The Use and Care manual says only a qualified service technician should remove the front cover RTGH-3 manual, p. 49.

Check these first

  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 99 is still shown, close the tap, turn the heater off, unplug it for about 30 seconds and plug it back in. Keep the heater turned off while you check the venting RTGH-3 manual, pp. 66, 74.
  3. Outside, remove anything blocking the air intake or the vent exhaust. Leave at least 12 in. (30 cm) between the air intake opening and any obstruction RTGH-3 manual, pp. 66, 75; RTG-3 manual, p. 68; RTG-R-3 manual, p. 65.
  4. Restart the heater, open a hot tap and check the display. If 99 is still shown, turn the heater off, write down the code and call for service RTGH-3 manual, p. 74. The Use and Care manuals do not say whether their reset sequence clears a hard lockout.

Do not run the heater if the vent system shows signs of leaking exhaust RTGH-3 manual, p. 64; RTG-3 manual, p. 66; RTG-R-3 manual, p. 63.

When to call a licensed technician

  • Code 99 that stays after the openings are clear and the heater has been unplugged. The hard lockout reset is done behind the front cover, on the control board AP21822 tech manual, p. 61.
  • Vent pipes that are loose or not connected properly at the termination RTGH-3 manual, p. 75.
  • Any work on the vent run. The vent pipe and its length limits differ by series: RTGH-3 uses 2 or 3 in. pipe RTGH-3 manual, pp. 20–21, RTG-3 and RTG-R-3 direct-vent models use 3 in./5 in. Category III coaxial stainless steel or manufacturer-approved concentric vent pipe RTG-3 manual, pp. 21–22; RTG-R-3 manual, pp. 21–22.
  • The yearly vent inspection RTGH-3 manual, p. 64; RTG-3 manual, p. 66; RTG-R-3 manual, p. 63.

Notes for different models

On Ruud Tankless Mid-Efficiency heaters, 99 means something else. Their chart prints it with 61 as a faulty blower motor and sends it to a dealer or qualified service technician; the venting row on that chart is 05 Tankless Water Heater Use and Care Manual AP18000-2, p. 26. On those heaters the chart’s answer to 99 is a service call, not the venting checks above.

IKONIC heaters report a venting blockage as A090 IKONIC Use and Care Manual, p. 107.

Related Rheem codes

  • 90 “Air intake or vent exhaust opening may be blocked.”
  • 10 “Incorrect inlet air volume”
  • 61 “Faulty blower motor.”

All Rheem codes

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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 (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.