HVACopediaRinnai · Tankless water heater
In Use solid In Use light steady
What the display is showing
The In Use light on the integrated controller stays on steadily while the burner is lit and hot water is flowing. Normal operation. On units with an external pump this is one of three In Use patterns.
Applies to: Rinnai SENSEI tankless (RU, RUR, RSC, CU) and SENSEI RX/CX (RX, RXP, CX, CXP)
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
30 models in SENSEI RX/CX, SENSEI
Other codes on the same units
- FF Maintenance performed (history marker)
- In Initial setting: indoor installation
- In Use fast flash In Use light rapid flash
- In Use slow flash In Use light slow flash
- LC Scale build-up in heat exchanger (LC, LC0–LC9, 00)
- LPG Initial setting: propane (LPG)
- Lock key Controller locked (key symbol)
- Mute Controller key beeps on/off
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Source: Rinnai N-Series Residential (100000467) / with Pump (100000508) / Commercial (100000504) / RSC SENSEI (100000773) Installation and Operation Manuals, 5.3.3 In Use Light p.70; Rinnai SENSEI RX Residential Installation and Operation Manual (100000839), 5.3 p.56. Summarized in our own words; check the original manual for your model.
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.