HVACopediaRinnai · Tankless water heater
25 Condensate pump failure or clogged drain
What the control is telling you
Triggered when the condensate float/safety switch closes because condensate has backed up, or when the accessory condensate pump stops working.
Applies to: SENSEI Series; SENSEI RX/CX Series; Non-SENSEI Series
Likely causes
- No power to the condensate pump
- External condensate pump not working
- Clogged or frozen drain line
- Loose or damaged wiring between pump/trap and PC board
- Missing air gap in drain line
- Restricted condensate trap
Test and repair steps
- Confirm the condensate pump has power.
- Check that the external (third-party) pump operates correctly.
- Make sure the drain line is not clogged or frozen.
- Inspect wiring from the pump and from the condensate trap back to the PC board for loose, damaged or broken connections.
- Confirm the drain line includes an air gap.
- Inspect the condensate trap for restrictions.
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
- 18 Gas valve air/fuel adjustment limit reached
- 19 Electrical grounding / DC circuit short
- 21 PC board data transfer error
- 22 Gas valve adjustment fault
- 30 Flammable vapor sensor activated or faulty
- 31 Burner thermocouple out of range
- 32 Outlet water temperature thermistor fault
- 33 Heat exchanger thermistor fault
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.34. 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.