HVACopediaRinnai · Tankless water heater
05 Bypass flow control device fault
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
- 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).
- SENSEI If readings are out of range, replace the bypass flow control device.
- 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.
- RH180 Clean the air filter.
- 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.
- 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.
- 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.
- 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.
- RH180 If code 05 remains after these steps, follow the code 10 procedure.
Settings for these units
RSC supply connection sizes · SENSEI
| Connection | Size |
|---|---|
| Gas | 3/4 in. NPT |
| Cold inlet | 3/4 in. NPT |
| Hot outlet | 3/4 in. NPT |
| Condensate drain | 1/2 in. NPT |
| Pressure relief valve | M33 thread |
The PRV and its adapter come in the box; PRV must be rated 150 psi and at least the heater Btu/h.
Condensate drain line must stay at least 1/2 in. over its whole length.
RSC water quality limits · SENSEI
| Contaminant | Maximum level |
|---|---|
| Total hardness | Up to 200 mg/L |
| Aluminum | Up to 0.2 mg/L |
| Chlorides | Up to 250 mg/L |
| Copper | Up to 1.0 mg/L |
| Dissolved CO2 | Up to 15.0 mg/L |
| Iron | Up to 0.3 mg/L |
| Manganese | Up to 0.05 mg/L |
| pH | 6.5 to 8.5 |
| TDS | Up to 500 mg/L |
| Zinc | Up to 5 mg/L |
Damage from water above these limits is not covered by warranty.
Hard water should be treated; use the Service Soon (SS) reminder (parameter 03) for flushing intervals.
- RSC clearances to combustibles · SENSEI
- RSC temperature settings available · SENSEI
- RUCS/RUS unit clearances · Non-SENSEI
- RUCS/RUS water quality limits · Non-SENSEI
- Water quality limits - RU/RUR/CU · SENSEI
- Clearances - RU/RUR/CU · SENSEI
Models that show this code
79 models in Non-SENSEI, RH180 hybrid, SENSEI
Other codes on the same units
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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.
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.