HVACopediaNoritz · Tankless water heater · Domestic hot water
Water route: main and bypass servo by set temperature
What happens, in order
- Flow passes through the main water control servo
- If set temperature is 120 F or lower, both bypass and main servos stay open
- If set temperature is 125 F or higher, the bypass closes and the main stays open
- Bypass or main servo problems show as 65 (main) or 66 (bypass)
- Compare MM31 (outlet) and MM32 (heat exchanger) to spot a stuck bypass servo
Timings and thresholds
| Item | Value |
|---|---|
| Set temp 120 F or lower | bypass open, main open |
| Set temp 125 F or higher | bypass closed, main open |
Codes you may see during this
Applies to: Noritz residential tankless (NRC / NRCP and older)
Models
More Noritz tankless water heater sequences
- On-demand heating cycle · Domestic hot water
- Auto Learning recirculation · Pump/purge
- Other recirculation modes · Pump/purge
- Freeze prevention heaters and pump · Freeze protection
Related
Take it to the job
Sequences of operation, error codes and tips work offline in the HVACopedia app.
Source: Noritz Residential Level 2 Maintenance and Troubleshooting training (R2 Printable V1), water control route page; Premix R2 training. Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
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.