HVACopediaRinnai · Tankless water heater
SS Service Soon alert (also listed as 55)
What the control is telling you
Time-based service reminder configured at installation (Parameter 03). It means the unit is due for service and the heat exchanger should be flushed.
Applies to: SENSEI Series, SENSEI RX/CX Series
Likely causes
- Service interval set in Parameter 03 has elapsed
- Heat exchanger due for flushing (scale risk with hard water)
Test and repair steps
- Flush the heat exchanger to prevent damage (owner's manual section 6.3, Flushing the Heat Exchanger).
- Treat hard water to prevent scale build-up and heat exchanger damage.
- SENSEI Reset SS by pressing the On/Off button on the temperature controller five times within five seconds.
- SENSEI RX/CX Reset SS by pressing and holding the "A" button until SS clears.
- Confirm Parameter 03 is set as intended A = not active, B = 0.5 yr, C = 1 yr, D = 2 yrs (see owner's manual section 4.12 for SENSEI, 4.13 for SENSEI RX/CX).
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
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.66. 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.