HVACopediaRinnai · Combi boiler
670 Three-way valve fault
What the control is telling you
The 3-way (DHW/CH) 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
- Loose, broken or damaged 3-way valve wiring
- Wet harness or connectors
- Poor CH system water quality
- Valve stuck or mispositioned
- Failed 3-way valve assembly
Test and repair steps
- Inspect the 3-way valve harness back to the PC Board for loose, broken or damaged connections and make sure it is dry.
- Check central heating system water quality.
- Warning: Live-voltage testing is dangerous and should only be done by qualified technicians using proper precautions.
- Read the valve position in performance data #15 (0 = mid, 1 = DHW, 2 = CH).
- At CN12, grey pin #16 to brown pin #18: under 1 VDC when fully open or closed, 4–6 VDC in mid position. Orange pin #6 to grey pin #16 should be 11–14 VDC.
- At CN12, pink pin #4 to red pin #3 and white pin #2 to blue pin #1 should each read 40–60 Ω.
- Replace the 3-way valve assembly if readings are out of spec or the fault remains.
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Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.37. Summarized in our own words; check the original manual for your model.
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