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Rinnai · Boiler

520 Gas solenoid valve circuit – flame after valve close

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

What the control is telling you

The flame rod still senses flame after the board has commanded the gas valve to close.

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

Likely causes

  • Loose or damaged gas solenoid valve wiring
  • Gas solenoid out of resistance/voltage spec
  • Wet flame rod from a leaking heat exchanger
  • Failed gas valve and venturi assembly
  • Failed PC Board

Test and repair steps

  1. Warning: Shut off power and gas supply before servicing.
  2. Inspect the gas solenoid valve harness for loose or damaged terminals.
  3. At PC Board connector CN8, measure black pin #11 to yellow pin #12: 15–25 ohms or 11–14 VDC.
  4. With the gas shut-off closed, pull and inspect the flame rod for moisture; if wet, check the heat exchanger for leaks and replace it if leaking. Always fit a new flame rod gasket on reinstall.
  5. Press PC Board buttons SW1 and SW2 together until ECL shows on the display to reset code 520 and return to normal operation.
  6. If 520 returns after the ECL reset, replace the gas valve and venturi assembly, then do the ECL reset again.
  7. If the code persists after replacing the gas valve and venturi assembly, replace the PC Board.

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Source: Rinnai Troubleshooting I-Series Plus Boiler Diagnostic Codes (800000375), p.30. 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.