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Rinnai · Combi boiler

661 Bypass valve fault

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

What the control is telling you

The bypass control valve is in the wrong position, stuck, 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

  • Bypass valve stuck or mispositioned
  • Loose, broken or damaged bypass valve wiring
  • Wet harness or connectors
  • Failed bypass valve assembly
  • 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 returns.
  2. Inspect the bypass valve harness back to the PC Board for loose, broken or damaged connections and make sure it is dry.
  3. Warning: Turn off electrical supply before taking resistance readings.
  4. At PC Board connector CN12 red pin #13 to pink pin #14 and white pin #12 to blue pin #11 should each read 40–60 Ω.
  5. Replace the bypass valve assembly.
  6. If a new bypass valve 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.