HVACopediaRinnai · Tankless water heater
16 Outlet water over-temperature safety shutdown
What the control is telling you
Safety shutdown triggered because the outgoing water temperature went above 203°F (95°C).
Applies to: SENSEI Series; SENSEI RX/CX Series; Non-SENSEI Series
Likely causes
- Restricted air flow at the vent terminal
- Fan not operating properly
- Check valve behind fan motor stuck and restricting air flow
- Debris in combustion chamber or exhaust piping
- Blocked heat exchanger
- Unit set to wrong gas type (e.g. Parameter 10 incorrect)
- Faulty gas valve or fan motor assembly
Test and repair steps
- Look for anything restricting air flow around the vent terminal.
- Confirm the fan operates correctly.
- Make sure the check valve behind the fan motor is not stuck and blocking air flow.
- Check the combustion chamber and exhaust piping for foreign material.
- Check the heat exchanger for blockage.
- Confirm the unit is configured for the gas type on its rating plate.
- SENSEI / SENSEI RX/CX Check Parameter 10 (A = Natural Gas, B = Propane). On RX/CX models, Parameter 10 can only be changed within 20 minutes of a power reset.
- If the fault persists, replace the gas valve assembly, then the fan motor assembly if needed.
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
- RX supply connection sizes · SENSEI RX/CX
- RX water quality limits · SENSEI RX/CX
- RX water treatment and flushing by hardness · SENSEI RX/CX
- RX clearances to combustibles · SENSEI RX/CX
Models that show this code
89 models in Non-SENSEI, RH180 hybrid, SENSEI RX/CX, SENSEI
Other codes on the same units
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.27. 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.