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Noritz · Tankless water heater

20 High limit switch tripped

High severity Noritz EZNoritz NRCRNoritz CDVNoritz NRC/NRCP

What the control is telling you

The high limit switch on the heat exchanger opened because of overheating. Same meaning on all families.

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

Likely causes

  • Scale deposits in the heat exchanger
  • Poor combustion
  • Bad wiring or a failed high limit switch

Test and repair steps

  1. Descale the heat exchanger and clean the inlet filter; check water hardness.
  2. Check combustion inlet gas pressure, venting, and a clean fan/venturi and burner on premix units.
  3. Turn off power and check the high limit switch wiring and connector for damage.
  4. Check the switch for continuity at room temperature; replace if open.
  5. Warning: Do not jumper the high limit switch.

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), 14, 16, 20 error codes, p.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.