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Noritz · Tankless water heater

16 Abnormally high outlet temperature

High severity Noritz EZNoritz NRCRNoritz CDVNoritz NRC/NRCP

What the control is telling you

The outlet water got hotter than allowed. Same meaning on all families. Most common cause is scale in the heat exchanger and water parts; wrong gas type is also listed for premix units.

Applies to: All Noritz residential tankless (EZ, NRCR, NCC199CDV, NRC/NRCP)

Likely causes

  • Hard water scale built up in the heat exchanger, water control parts, or both
  • Wrong gas type (premix units)
  • Clogged inlet filter screen reducing flow

Test and repair steps

  1. Check water hardness; Noritz requires treatment above 12 gpg (200 mg/L).
  2. Descale the heat exchanger with the descale kit (1 hour, 50/50 mix of water and calcium/lime/rust remover).
  3. Clean the cold water inlet filter (and recirculation filter on NRCR).
  4. Premix confirm the gas type setting matches the gas supplied and that LP conversion was done correctly (sticker on unit).
  5. Use MM31 (outlet) and MM32 (heat exchanger) temperature to confirm readings during a draw.
  6. Advise a water softener or scale inhibitor to prevent repeat scale.

Settings for these units

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Source: Noritz EZ/NRCR/CDV Level 2 Maintenance & Troubleshooting (Premix R2 V2), 16 & 20 error codes, p.14; Noritz Residential Level 2 Maintenance & Troubleshooting (NRC/NRCP and older, R2 V1), Descaling/flushing and 14, 16, 20 error codes, p.3, 8; Noritz NRCR Pro training (NRCR92/NRCR111, Printable V3), Poor water quality issues, p.32. 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.