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Noritz · Tankless water heater

902 Combustion abnormality (sub-code of 90)

High severity Noritz EZNoritz NRCR

What the control is telling you

EZ/NRCR owner's guide lists 901 and 902 with 90: air supply or exhaust may be blocked, low gas pressure, or condensate drain clogged.

Applies to: Noritz EZ111/EZ98/EZ71 and NRCR111/NRCR92

Likely causes

  • Clogged air supply (indoor air) or exhaust
  • Low gas supply pressure
  • Clogged or frozen condensate drain line

Test and repair steps

  1. Check the air supply opening and exhaust vent for blockage.
  2. Check inlet gas pressure (NG 3.5-10.5 in. WC, LP 8-14 in. WC).
  3. Check the condensate line for clogs or ice.
  4. Follow the code 90 steps for MM31/MM32 checks and fan/venturi cleaning.

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Source: Noritz EZ/NRCR Owner's Guide (Rev. 10-25), Checking for error conditions, p.31. Summarized in our own words; check the original manual for your model.

Homeowner looking at this code? See what it means for you and when to call a technician.

For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.