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Rinnai · Tankless water heater

FE Flammable vapors detected

Critical severity RH180 hybrid

What the control is telling you

The flammable vapor sensor on the RH180 hybrid unit has detected flammable vapors, or the sensor/its circuit is faulty.

Applies to: RH180 (hybrid tank-tankless, Non-SENSEI Series)

Likely causes

  • Flammable vapors present near the water heater
  • Loose, damaged or broken flammable vapor sensor wiring
  • Sensor improperly mounted or damaged
  • Failed flammable vapor sensor
  • Faulty PC board

Test and repair steps

  1. Warning: Leave the room or space until safety personnel confirm it is safe and all flammable vapors have been removed.
  2. Warning: Only technicians qualified to service gas water heaters should continue.
  3. Disconnect power to the water heater.
  4. Remove the front panel and inspect the flammable vapor sensor and its harness back to the PC board for loose, damaged or broken wires or connectors.
  5. Confirm the sensor is mounted correctly and is not damaged.
  6. Only once you are sure no vapors are present: restore power and gas, open a tap to fire the unit and check sensor voltages at PCB connector D1 (Red–Black pins 1–6: 1.9–2.1 VDC; White–Yellow pins 4–3: 25.5–39.5 VDC).
  7. If FE returns and no flammable vapors are present, replace the flammable vapor sensor.
  8. Replace the PC board.

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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.63. 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.