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Rinnai · Combi boiler

651 Water flow control valve fault

Medium severity I-Series Plus 150K and smallerI-Series Plus 175K and higher

What the control is telling you

The water flow control valve is out of position, not moving, or the PC Board cannot communicate with it.

Applies to: I-Series Plus Combi boilers — 150K BTU and smaller and 175K BTU and higher

Likely causes

  • Valve stuck or not in correct position
  • Loose or damaged servo connectors/harness
  • Wet wiring or connectors
  • Failed water flow control servo
  • Failed PC Board

Test and repair steps

  1. Cycle power to see if the code clears, then run the unit several times to see if it comes back.
  2. Inspect the flow servo connectors and harness between the valve and PC Board, and make sure they are dry.
  3. Warning: Turn off electrical supply before taking resistance readings.
  4. At PC Board connector CN12 white pin #8 to blue pin #7 and red pin #9 to pink pin #10 should each read 40–60 Ω.
  5. At CN12, grey pin #15 to brown pin #17: under 1 VDC with the valve fully open, 4–6 VDC with it fully closed.
  6. Replace the water flow control servo.
  7. If the new servo does not clear the code, replace the PC Board.

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Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.36. 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.