Noritz · Tankless water heater

66 Bypass water control servo abnormality

Medium severity Noritz EZNoritz NRCRNoritz CDVNoritz NRC/NRCP

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
Operation panel menu settings and defaults · Noritz EZ, Noritz NRCR
Water quality limits · Noritz EZ, Noritz NRCR

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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.