How House Works

Noritz 90 (combustion abnormality): what to check

By How House Works EditorialBased on Noritz manualsChecked against sources Updated

Noritz display

90

“(1) [When supplying combustion air from the indoors] The air supply vent may be clogged. (2) Exhaust vent may be clogged. (3) Abnormal combustion, low gas supply pressure. (4) Condensate drain line may be clogged.”

EZ, NRCR · EZ/NRCR Owner's Guide Rev. 10/25, p. 31; EZ/NRCR Owner's Guide Rev. 01/24, p. 25; EZ Owner's Guide SBB8163-2, p. 18; EZ Owner's Guide SBB80T9-2, p. 28; NRCR Owner's Guide Rev. 04/21, p. 20
Owner checks, then technician

Quoted from the EZ/NRCR Owner's Guide Rev. 10/25, which prints 90, 901 and 902 in this row (p. 31); the 2024 guide prints 90, 901 and 908 (EZ/NRCR Owner's Guide Rev. 01/24, p. 25). Other guides list fewer causes. NRC98, 2017 NRC111, NERC, NRC83 and NRC1111: causes (1) and (3) (NRC98 Owner's Guide Rev. 01/17, p. 28; NRC83/NRC98 Owner's Guide Rev. 03/13, p. 27). NR98 (2020) and NR981: “[NR981-SV] The air inlet filter may be clogged.” and cause (3) (NR98 Owner's Guide Rev. 11/20, p. 26; NR981 Owner's Guide Rev. 03/13, p. 27). NR83, NR71DVC, NR50/NR66/NR71, NR111, 2009 NR98 and 2009 NRC111: only “Abnormal combustion, low gas supply pressure” (NR83 Owner's Guide Rev. 11/20, p. 25; NR50/NR66/NR71 Owner's Guide Rev. 01/11, p. 26; NRC111 Owner's Guide Rev. 09/09, p. 27). On EZTR40, NRC661A/NRC711, NRC661, NR501/NR662 and NER66OD heaters the display shows 901, 902, 903 or 908 and the optional remote shows 90 (EZTR40 Owner's Guide Rev. 01/17, p. 24). EZ technical sheets: “Combustion abnormality (Unit shuts off)”.

What it means

Noritz calls 90 a combustion abnormality EZ Installation Manual Rev. 10/25, p. 61, and its technical sheet adds that the unit shuts off EZ Technical Sheet FPFK081, p. 1. The EZ/NRCR Owner’s Guide Rev. 10/25 lists four possible causes: a clogged air supply vent when combustion air comes from indoors, a clogged exhaust vent, low gas supply pressure, and a clogged condensate drain line p. 31. The NRC and NR guides list fewer causes; see the notes at the end.

Check these first

Before any maintenance, turn the heater off at the operation panel, app or remote controller and let it cool EZ/NRCR Owner’s Guide Rev. 10/25, p. 3.

  1. If the heater takes combustion air from the room, check the air supply vent for dust, oil or other build-up and remove it with a vacuum cleaner or a damp towel. Do not completely remove the inlet screen and the air screen EZ/NRCR Owner’s Guide Rev. 10/25, p. 26.
  2. Check the exhaust vent and its terminal for blockage, dust or soot EZ/NRCR Owner’s Guide Rev. 10/25, pp. 26, 31. Noritz says not to use the heater if the intake or exhaust pipe is displaced, has holes, is clogged or is corroded EZ/NRCR Owner’s Guide Rev. 10/25, p. 2.
  3. On EZ and NRCR heaters, check whether the condensate drain line is clogged or frozen EZ/NRCR Owner’s Guide Rev. 10/25, p. 31.
  4. On NRC98, 2017 NRC111, NERC, NRC83 and NRC1111 heaters, the 90 row asks you to clean the air supply vent NRC98 Owner’s Guide Rev. 01/17, p. 28. The NRC98 guide’s instructions match step 1 and say not to permanently remove the inlet screen NRC98 Owner’s Guide Rev. 01/17, p. 21.
  5. If the display continues, contact the nearest Noritz agent EZ/NRCR Owner’s Guide Rev. 10/25, p. 31 or Noritz America Technical Support at 1-866-766-7489 EZ/NRCR Owner’s Guide Rev. 10/25, p. 32.

The owner’s guides give no reset step for 90.

When to call a licensed technician

  • Gas supply pressure. Every guide that lists low gas pressure for 90 says to have a professional check it EZ/NRCR Owner’s Guide Rev. 10/25, p. 31; NR83 Owner’s Guide Rev. 11/20, p. 25. The pressure ranges are on the code 11 page.
  • No water comes out of the end of the condensate drain line. A qualified service technician must clean the line EZ/NRCR Owner’s Guide Rev. 10/25, p. 25.
  • A damaged vent, or one that has to be taken apart. The venting system must be examined periodically for leaks or corrosion by a qualified service technician EZ Installation Manual Rev. 10/25, p. 69.
  • 908 on an EZ or NRCR heater covered by the 01/24 guide. The technical sheet says it means an internal lock has been activated EZ Technical Sheet FHCK080, p. 1.
  • The heater still shows 90 after these checks. Noritz’s sheet for service technicians adds checks that the condensate drain pipe slopes down and that the unit settings on the circuit board are right, and gives its reset as disconnecting and reconnecting power EZ Technical Sheet FPFK081, p. 1.

Notes for different models

  • EZ and NRCR: the 2025 guide prints 90, 901 and 902 in one row, the 2024 guide 90, 901 and 908 EZ/NRCR Owner’s Guide Rev. 10/25, p. 31; EZ/NRCR Owner’s Guide Rev. 01/24, p. 25. The 2021 guides list 90 alone EZ Owner’s Guide SBB8163-2, p. 18; NRCR Owner’s Guide Rev. 04/21, p. 20.
  • NRC98, 2017 NRC111, NERC, NRC83 and NRC1111: two causes, the air supply vent and low gas supply pressure NRC98 Owner’s Guide Rev. 01/17, p. 28.
  • NR98 (2020) and NR981: the first cause is labeled “[NR981-SV] The air inlet filter may be clogged.” The NR98 guide’s action for it is to clean the air supply vent, the NR981 guide’s is to clean the air inlet filter NR98 Owner’s Guide Rev. 11/20, p. 26; NR981 Owner’s Guide Rev. 03/13, p. 27. The NR98SV has an air inlet filter that must not be removed; if it is removed or damaged, contact Noritz America NR98 Owner’s Guide Rev. 11/20, p. 21.
  • NR83, NR71DVC, NR50/NR66/NR71, NR111, the 2009 NR98 and the 2009 NRC111: low gas supply pressure is the only cause, with a professional check and a call to the nearest Noritz agent. These guides give no owner check for 90 NR83 Owner’s Guide Rev. 11/20, p. 25; NR50/NR66/NR71 Owner’s Guide Rev. 01/11, p. 26.
  • EZTR40, NRC661A/NRC711, NRC661, NR501/NR662 and NER66OD: the display shows 901, 902, 903 or 908, and the optional remote shows 90 EZTR40 Owner’s Guide Rev. 01/17, p. 24. See the 903 page.

Related Noritz codes

  • 903 “Abnormal combustion. The air inlet filter may be clogged.”
  • 902 “Abnormal combustion, low gas supply pressure.”
  • 99 “Abnormal combustion”
  • 29 “Clogging of condensate trap or drain pipe”

All Noritz codes

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Sources

  1. NORITZ America Corporation. EZ/NRCR Owner's Guide Rev. 10/25. SBB81M1, Rev. 10/25; cover title: Condensing Tankless Gas Water Heater Owner's Guide; covers EZ111DV, NRCR111DV, EZ98DV, NRCR92DV and EZ71DV (GQ-...-FF-1 US models); EZTR50 and EZTR75 are named only in the warranty table (p. 36); p. 1 is the unnumbered cover. Accessed Oct 12, 2026.
  2. NORITZ America Corporation. EZ/NRCR Owner's Guide Rev. 01/24. SBB81HC, Rev. 01/24; cover title: Condensing Tankless Gas Water Heater Owner's Guide; covers the 2024 EZ111DV, NRCR111DV, EZ98DV, NRCR92DV and EZ71DV (GQ-...-FF US models). Accessed Oct 12, 2026.
  3. NORITZ America Corporation. EZ Owner's Guide SBB8163-2. SBB8163-2, Rev. 04/21; covers EZ111DV (GQ-C3260WX-FF US) and EZ98DV (GQ-C2860WX-FF US). Accessed Oct 12, 2026.
  4. NORITZ America Corporation. EZ Owner's Guide SBB80T9-2. SBB80T9-2, Rev. 04/21; covers EZ111DV (GQ-C3259WX-FF US) and EZ98DV (GQ-C2859WX-FF US). Accessed Oct 12, 2026.
  5. NORITZ America Corporation. NRCR Owner's Guide Rev. 04/21. SBB8167-3, Rev. 04/21; covers NRCR111DV (GQ-C3260WXQ-FF US) and NRCR92DV (GQ-C2660WXQ-FF US). Accessed Oct 12, 2026.
  6. NORITZ America Corporation. EZTR40 Owner's Guide Rev. 01/17. SBB809K-2, Rev. 01/17; covers NRC663-FSV (EZTR40). Accessed Oct 12, 2026.
  7. NORITZ America Corporation. NRC98 Owner's Guide Rev. 01/17. SBB80JP-3, Rev. 01/17; covers NRC98DV (GQ-C2857WS-FF US) and NRC98OD (GQ-C2857WS US). Accessed Oct 12, 2026.
  8. NORITZ America Corporation. NR98 Owner's Guide Rev. 11/20. SBB80J3-4, Rev. 11/20; covers NR98OD (GQ-2857WX US), NR98DVC (GQ-2857WX-FFA US) and NR98SV (GQ-2857WX-F US). Accessed Oct 12, 2026.
  9. NORITZ America Corporation. NR83 Owner's Guide Rev. 11/20. SBB80YQ-2, Rev. 11/20; covers NR83DVC (GQ-2457WS-FFA US) and NR83OD (GQ-2457WS US). Accessed Oct 12, 2026.
  10. NORITZ America Corporation. NR50/NR66/NR71 Owner's Guide Rev. 01/11. SBA8654, Rev. 01/11; covers NR71-SV, NR71-OD, NR66-SV, NR66-OD and NR50-OD. Accessed Oct 12, 2026.
  11. NORITZ America Corporation. NR981 Owner's Guide Rev. 03/13. SBA8893-1, Rev. 03/13; covers NR981-OD, NR981-DVC and NR981-SV. Accessed Oct 12, 2026.
  12. NORITZ America Corporation. EZ Technical Sheet FPFK081. Sheet code FPFK081, no revision or date printed; 2025 EZ111DV, EZ98DV and EZ71DV (GQ-...-FF-1 US); a service document filed under Field Manual in Noritz's Technical Literature; no page numbers printed, p. 1 is the PDF page. Accessed Oct 12, 2026.
  13. NORITZ America Corporation. EZ Technical Sheet FHCK080. Sheet code FHCK080, no revision or date printed; 2024 EZ111DV, EZ98DV and EZ71DV (GQ-...-FF US); a service document; no page numbers printed, p. 1 is the PDF page. Accessed Oct 12, 2026.
  14. NORITZ America Corporation. EZ Installation Manual Rev. 10/25. SBB81M3-1, Rev. 10/25; cover title: Condensing Tankless Gas Water Heater Installation Manual; covers EZ111DV, EZ98DV and EZ71DV (GQ-...-FF-1 US); linked from the EZTR50 and EZTR75 product pages, which the manual does not name. Accessed Oct 12, 2026.