HVACopediaRinnai · Tankless water heater
dES Descaling (flush) mode
What the display is showing
On RX/CX units, dES is the first screen when button B on the PC board is pressed once with the controller off. Pressing A then starts the descaling (vinegar flush) cycle and dES blinks. The same screen is the first step of the venturi/gas valve reset sequence used for codes 17 and 52.
Applies to: Rinnai SENSEI RX/CX tankless (RX, RXP, CX, CXP)
What to do
- Remove the front panel and locate pushbuttons A and B on the PC board (controller blank).
- Press B for 1 second and release when dES appears.
- Press A dES starts blinking and the flush cycle is running.
- Circulate vinegar through the unit; the display then counts down from 60 (minutes), shows rnS (rinse), then End.
Settings for these units
RX supply connection sizes · SENSEI RX/CX
| Connection | Size |
|---|---|
| Gas | 3/4 in. MNPT |
| Cold inlet | 3/4 in. MNPT |
| Hot outlet | 3/4 in. MNPT |
| Condensate drain | 1/2 in. MNPT |
Vent connection: 2 in. nominal PVC/CPVC/PP or 3 in./5 in. concentric.
Full specs (input, flow, weight) are only on each model's spec sheet, not in this manual.
RX water quality limits · SENSEI RX/CX
| 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 |
Water damage beyond these limits is not covered by warranty.
- RX water treatment and flushing by hardness · SENSEI RX/CX
- RX clearances to combustibles · SENSEI RX/CX
- RX temperature settings available · SENSEI RX/CX
Models that show this code
10 models in SENSEI RX/CX
Other codes on the same units
- Priority light Priority light on (this controller is in charge)
- SE Cascade diagnostic display (error on secondary unit)
- SEt Initial settings not yet confirmed
- SS Service Soon alert (also listed as 55)
- nG Initial setting: natural gas
- rnS Descaling finished, rinse now
- t Venturi reset sequence: step t
- °C/°F Temperature scale switch (Celsius / Fahrenheit)
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
Source: Rinnai SENSEI RX Residential Installation and Operation Manual (100000839), 6.3 Flushing the Heat Exchanger, Quick-Flush p.67-68; Rinnai Troubleshooting TWH Diagnostic Codes (100000652), Code 17 reset table p.29. 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.