HVACopediaNoritz · Tankless water heater
66 Bypass water control servo abnormality
What the control is telling you
The board cannot communicate with or position the bypass water control servo. Same meaning on all families.
Applies to: All Noritz residential tankless (EZ, NRCR, NCC199CDV, NRC/NRCP)
Likely causes
- Debris or scale in the bypass servo
- Failed servo
- Wiring/connector fault
- Circuit board fault
Test and repair steps
- Turn off power and check the bypass servo connector and wiring.
- Compare MM32 (heat exchanger temp) with MM31 (outlet temp): a big gap (e.g. 140 vs 100) points to a stuck or failed bypass servo.
- CDV run Trial Operation for the bypass servo in the EZ Start Plus app.
- Remove the servo and clear debris or scale; replace if it does not move.
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
- 061 Recirculation abnormality (sub-code of 06)
- 062 Recirculation abnormality (sub-code of 06)
- 63 Recirculation abnormality (no recirculation flow)
- 65 Main water control servo abnormality
- 73 Circuit board setting abnormality
- 90 Combustion abnormality
- 91 Gas conversion not done correctly
- 901 Combustion abnormality (sub-code of 90)
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Source: Noritz EZ/NRCR/CDV Level 2 Maintenance & Troubleshooting (Premix R2 V2), 65 & 66 error codes and MM32, p.15, 21; Noritz Residential Level 2 Maintenance & Troubleshooting (NRC/NRCP and older, R2 V1), 65 & 66 error codes, p.9. 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.