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Rinnai · Tankless water heater

05 Bypass flow control device fault

Medium severity Non-SENSEIRH180 hybridSENSEI

What the control is telling you

A fault with the bypass flow control device (bypass valve). On RH180 models this code is tied to restricted airflow through the air filter, vent, fan or burner/heat exchanger.

Applies to: SENSEI series, non-SENSEI series and RH180 hybrid tank-tankless

Likely causes

  • Bypass flow control device or bypass valve has failed
  • Bypass device coil resistance out of range (SENSEI)
  • RH180: dirty air filter, or vent installed or blocked incorrectly
  • RH180: restricted fan wheel/housing, clogged burner orifices, or blocked heat exchanger fins

Test and repair steps

  1. SENSEI At PC Board connector "D", measure 44–52 Ω across red pin 15 and pink pin 13, and across white pin 17 and blue pin 19 (see the Electric Circuit Table in the Tech Sheet).
  2. SENSEI If readings are out of range, replace the bypass flow control device.
  3. Non-SENSEI (not RH180) Turn power off and back on, then open a hot water tap. If code 05 comes back, replace the bypass valve.
  4. RH180 Clean the air filter.
  5. RH180 Make sure the vent uses approved 4 in. B-Vent installed per Rinnai's instructions, has no obstructions, and has proper clearance at the termination.
  6. RH180 – CAUTION: Turn off power before removing the fan motor. Check the fan wheel and housing for restrictions, refit the fan, restore power and test.
  7. RH180 – WARNING: Turn off electrical, gas and water supply. Then check the manifold orifices for blockage and clear debris from the burner and air chambers.
  8. RH180 Check heat exchanger fins for build-up. Blow out the burner and fins at 120 PSI, or replace the heat exchanger if it will not clean. CAUTION: wear safety glasses and a mask.
  9. RH180 If code 05 remains after these steps, follow the code 10 procedure.

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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.10. 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.