HVACopediaRinnai · Tankless water heater
15 Venturi control fault
What the control is telling you
The PC board has detected a problem with the venturi control device (gas valve/venturi assembly), which regulates the air/gas mix delivered by the fan.
Applies to: SENSEI Series; SENSEI RX/CX Series
Likely causes
- Loose, damaged or broken gas valve or solenoid harness connections
- Black reed switch on rear of gas valve not seated correctly (SENSEI RX/CX)
- Venturi control device out of resistance/voltage spec
- Fan motor not operating properly
- Restricted air flow through intake or exhaust venting
- Failed gas valve assembly
Test and repair steps
- Cycle the main power to the water heater off and back on.
- Inspect the gas valve and solenoid harnesses for loose, damaged or broken connections.
- SENSEI RX/CX Confirm the black reed switch on the back of the gas valve is seated in its correct position.
- SENSEI At PC board connector D (D5), with 120 VAC connected, check Red pin 12 to Black pin 30 = 12–14 VDC; Brown pin 25 and Grey pin 23 to Black pin 30 should each read under 1 VDC.
- SENSEI Check coil resistance at connector D: Blue pin 5 to White pin 7 and Yellow pin 11 to Red pin 9 should each read 35–41 ohms. See Electric Circuit Table in Tech Sheet and wiring diagram.
- SENSEI RX/CX At connector CN10, Blue pins 3, 4, 5, 6 to Black pin 2 and Red pins 9, 10, 11, 12 to Black pin 1 should each read 350–550 ohms.
- SENSEI RX/CX At CN10, Black pin 14 to Black pin 1 should read 4–6 VDC. See Electric Circuit Table in Tech Sheet and wiring diagram.
- Confirm the fan motor runs correctly.
- Confirm air moves freely through the vent system intake and exhaust ports.
- If the fault remains, replace the gas valve assembly; if still unresolved, replace the fan motor.
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
30 models in SENSEI RX/CX, SENSEI
Other codes on the same units
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.26. 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.