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Noritz · Tankless water heater

10 Abnormal combustion (NRCR, gas supply related)

High severity Noritz NRCR

What the control is telling you

The NRCR training deck lists code 10 together with 90 as 'abnormal combustion' caused by an improperly sized gas line. The deck gives no other detail for 10.

Applies to: Noritz NRCR92 / NRCR111 (NRCR Pro)

Likely causes

  • Undersized gas line or gas meter
  • Water or debris in the gas line
  • Earthquake safety shutoff valve restricting gas

Test and repair steps

  1. Measure inlet gas pressure at low, moderate, high and worst-case demand; NG must stay 3.5-10.5 in. WC and LP 8-14 in. WC.
  2. Check the gas line size against the gas sizing table in the installation manual (see Specs); a 1/2 in. line only works with 8 in. WC or higher initial pressure.
  3. Check the meter size and look for water/debris or a restricting earthquake valve in the supply.
  4. Also check intake/exhaust and condensate drain as for code 90.
  5. If the code persists, contact Noritz technical support (866-766-7489).

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Source: Noritz NRCR Pro training (NRCR92/NRCR111, Printable V3), Gas line conditions, p.20. Summarized in our own words; check the original manual for your model.

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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.