HVACopediaNoritz · Tankless water heater
20 High limit switch tripped
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
- Descale the heat exchanger and clean the inlet filter; check water hardness.
- Check combustion inlet gas pressure, venting, and a clean fan/venturi and burner on premix units.
- Turn off power and check the high limit switch wiring and connector for damage.
- Check the switch for continuity at room temperature; replace if open.
- Warning: Do not jumper the high limit switch.
Settings for these units
Indoor clearances (required and recommended) · Noritz NRCR
| Location | Required | Recommended (service) |
|---|---|---|
| Top | 12 in. (300 mm) | 3 in. (76 mm) above and below exhaust |
| Front | 4 in. (100 mm) | 24 in. (610 mm) |
| Sides | 3 in. (76 mm) | 8 in. (203 mm) |
Required clearances apply to both combustible and non-combustible materials.
Recommended space is for service and quick access to gas and water shut-offs.
Operation panel menu settings and defaults · Noritz EZ, Noritz NRCR
| Setting | Options | Default |
|---|---|---|
| Max Set Temperature (power off) | 100-140 F in 5 F steps; 37-48 C, 50-60 C | 120 F / 50 C |
| Recirc ON/OFF | ON / OFF | OFF |
| Recirc Mode | Always OFF, Always ON, Manual Timer, Auto Learning (NRCR) | Always OFF |
| Vacation Mode | Active / Inactive | Inactive |
| Flow Meter Alarm | 10-60 gal (5 gal steps), 70-100 gal (10 gal steps), OFF | Alarm OFF |
| Drain Water (power off) | Start / Cancel | Cancel |
| Scale Flushing (power off) | Start / Cancel | Cancel |
| Audible Alarm | ON / OFF | ON |
| Screen Lock | Active / Inactive (4-digit password) | Inactive |
| Units (first 10 min after power-up, power off) | [F/gal/ft] or [C/L/m] | [F/gal/ft] |
| Power Saving Dis. / Backlight | ON-OFF / Power Save ON-OFF | ON / Power Save ON |
| Brightness / Contrast / Touch Sound | Bright-Normal-Dim-Dark / -15 to +15 / ON-OFF | Normal / Standard / ON |
Setting 125 F (55 C) or higher needs Max Set Temperature raised first; the panel warns about scald risk.
Default Settings resets everything in Settings except Screen Lock (hold OK about 5 s).
- Water quality limits · Noritz EZ, Noritz NRCR
Models that show this code
12 models in Noritz EZ, Noritz NRCR, Noritz CDV, Noritz NRC/NRCP
Other codes on the same units
- 11 Ignition failure (no flame detected)
- 12 Flame loss (repeated)
- 14 Thermal fuse failure
- 16 Abnormally high outlet temperature
- 29 Condensate collector water level abnormal
- 061 Recirculation abnormality (sub-code of 06)
- 062 Recirculation abnormality (sub-code of 06)
- 63 Recirculation abnormality (no recirculation flow)
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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.