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Rinnai · Combi boiler

400 Water pressure sensor communication fault

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

What the control is telling you

The PC Board has lost communication with the system water pressure sensor.

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

Likely causes

  • Loose, broken or damaged pressure sensor wiring harness
  • Water supply turned off or supply valves closed
  • Boiler pump not running
  • Incorrect sensor supply voltage from PC Board
  • Failed water pressure sensor

Test and repair steps

  1. Inspect the pressure sensor harness all the way back to the PC Board for loose, broken or damaged connections.
  2. Confirm the inlet water supply is on and every water supply valve is open.
  3. Confirm the boiler pump is operating.
  4. At PC Board connector CN8, check supply voltage between black pin #9 and red pin #5: should be 11–14 VDC.
  5. At CN8, measure millivolts between yellow pin #1 and black pin #9: about 655–745 mV at 0 psi, 2,155–2,245 mV at 29 psi (200 kPa), 3,655–3,745 mV at 58 psi (400 kPa).
  6. If wiring, supply and voltages check out but the fault remains, replace the pressure sensor.

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Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.28. Summarized in our own words; check the original manual for your model.

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