HVACopedia

Rinnai · Tankless water heater

66 Bypass flow servo fault

Medium severity SENSEI RX/CX

What the control is telling you

The bypass flow control device (servo) circuit is faulty on SENSEI RX/CX units.

Applies to: SENSEI RX/CX Series

Likely causes

  • Wet harness or connector
  • Bypass flow control device resistance out of range
  • Failed bypass flow control device
  • Faulty PC board

Test and repair steps

  1. Make sure the harness and connector are dry.
  2. Measure bypass flow control device resistance at PC board connector CN10: red #17–pink #18 = 40-60 Ω; blue #15–white #16 = 40-60 Ω (see Electric Circuit Table/wiring diagram).
  3. Per the manual if either reading is out of range, replace the PC board; otherwise replace the bypass flow control device.

Settings for these units

Save it for the next call

Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.

Open the app

Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.56. 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.