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Rinnai · Tankless water heater

18 Gas valve air/fuel adjustment limit reached

High severity SENSEI RX/CX

What the control is telling you

The Smart-Sense gas valve has hit its rich or lean air/fuel adjustment limit for the selected gas type, which should not happen in normal operation.

Applies to: SENSEI RX/CX Series

Likely causes

  • Wrong gas being supplied to the unit
  • Parameter 10 (Gas Type) set incorrectly
  • Incorrect gas valve parameters entered
  • Flame rod wire disconnected or damaged

Test and repair steps

  1. Confirm the correct gas (natural gas or propane) is being supplied.
  2. Check Parameter 10 (A = Natural Gas, B = Propane). It can only be changed within 20 minutes after a power reset.
  3. Verify or re-enter the gas valve parameters per 'Enter Gas Valve Parameters' in the Gas Valve Replacement Instructions (100000855).
  4. Confirm the flame rod wire is connected and undamaged.

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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.30. Summarized in our own words; check the original manual for your model.

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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.