HVACopediaRinnai · Tankless water heater
65 Water flow control device (servo) fault
What the control is telling you
The water flow control servo is faulty; the servo valve did not close during the bath fill function.
Applies to: SENSEI Series, SENSEI RX/CX Series, Non-SENSEI Series
Likely causes
- Loose, broken or damaged servo wiring
- Water flow control servo failed to close
- Failed water flow control servo
- Incorrect servo resistance or supply voltage at the PC board
Test and repair steps
- Inspect the harness from the water flow servo valve to the PC board for loose, broken or damaged connections.
- Cycle power off and on and see whether the code clears.
- Because the servo failed to close during bath fill, shut off the water flow right away and stop using the bath fill controller.
- Warning: Turn off the electrical, gas and water supply to the heater before continuing.
- Replace the water flow control servo.
- SENSEI At connector D: red #18–pink #20 = 44–52 Ω; white #16–blue #14 = 44–52 Ω; grey #30 (black near the board)–orange #12 = 12–14 VDC.
- SENSEI RX/CX At CN9: red #16–pink #17 and white #15–blue #14 = 40-60 Ω; grey #5–orange #9 = 11-13 VDC; grey #5–brown #13 = under 1 VDC with limiter on, 4-6 VDC with limiter off.
Settings for these units
RSC supply connection sizes · SENSEI
| Connection | Size |
|---|---|
| Gas | 3/4 in. NPT |
| Cold inlet | 3/4 in. NPT |
| Hot outlet | 3/4 in. NPT |
| Condensate drain | 1/2 in. NPT |
| Pressure relief valve | M33 thread |
The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.
Condensate drain line must stay at least 1/2 in. over its whole length.
RSC water quality limits · SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved CO2 | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
Damage from water above these limits is not covered by warranty.
Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.
- RSC clearances to combustibles · SENSEI
- RSC temperature settings available · SENSEI
- RX supply connection sizes · SENSEI RX/CX
- RX water quality limits · SENSEI RX/CX
- RX water treatment and flushing by hardness · SENSEI RX/CX
- RX clearances to combustibles · SENSEI RX/CX
Models that show this code
89 models in Non-SENSEI, RH180 hybrid, SENSEI RX/CX, SENSEI
Other codes on the same units
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.55. Summarized in our own words; check the original manual for your model.
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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.