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Rinnai · Tankless water heater

15 Venturi control fault

High severity SENSEI RX/CXSENSEI

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

  1. Cycle the main power to the water heater off and back on.
  2. Inspect the gas valve and solenoid harnesses for loose, damaged or broken connections.
  3. SENSEI RX/CX Confirm the black reed switch on the back of the gas valve is seated in its correct position.
  4. 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.
  5. 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.
  6. 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.
  7. 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.
  8. Confirm the fan motor runs correctly.
  9. Confirm air moves freely through the vent system intake and exhaust ports.
  10. If the fault remains, replace the gas valve assembly; if still unresolved, replace the fan motor.

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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.