Rinnai code 21: Data transfer or dip switch error
Continuous flow hot water system (Australia), tankless water heater (United States)
Settings data did not transfer, the control board parameters were not set, or a dip switch is set incorrectly.
This needs a licensed gas technician. There is nothing safe to check yourself. Leave the covers on and book a professional.
Only some models show this code. Check the list below.
What causes it
Australian gas continuous flow models
-
The settings data transfer did not finish, or the control board parameters were not set.
-
A dip switch on the control board was set incorrectly during installation.
Infinity Enviro 32 and Heavy Duty 32C
-
The settings data transfer did not finish, or the control board parameters were not set.
US tankless models
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The data transfer to a new control board did not complete, or its parameters were not programmed for the model.
How to read this code on your unit
Booking a licensed gas technician
Book a licensed gas technicianlicensed gas technician
- Turn the unit off and leave the covers on. Gas components must only be serviced by a licensed technician.
- Note the code, how often it appears, and the model and serial numbers from the rating label.
- Book a licensed gas technician and give them those details.
Models that show this code
41 models in 8 ranges
| Range | Models |
|---|---|
| Heavy Duty (commercial) | REU-AM3237WC (HD32e), REU-VCM2837FFC (HD28i), REU-VCM2837WC (HD28e), REU-NB3237WC-AK (Heavy Duty 32C), REU-NB3237FFC-AK, REU-NB3237WC-50-AK, REU-NB3237FFC-50-AK |
| Infinity | REU-AM3237W (Infinity 32), REU-AM2626WDL (Infinity 26 Touch), REU-AM2626WD (Infinity 26), REU-AM2024WD (Infinity 20), REU-AM1620WD (Infinity 16), REU-AM1220WD (Infinity 12), REU-A2626WB (B26), REU-A2024WB (B20), REU-A1620WB (B16) |
| Infinity B | REU-BM2626W (Infinity B26), REU-BM2024W (Infinity B20), REU-BM1620W (Infinity B16), REU-BM1220W (Infinity B12) |
| Infinity Enviro | REU-E2626W (Infinity Enviro 26), REU-E1620W (Infinity Enviro 16), REU-NB3237W-AK (Infinity Enviro 32), REU-NB3237W-50-AK |
| Infinity internal | REU-VCM2837FF (Infinity 28i) |
| SENSEI commercial | CU199i (REU-N3237FFC-US), CU160i (REU-N2530FFC-US), CU199e (REU-N3237WC-US), CU160e (REU-N2530WC-US) |
| SENSEI residential | RU199i (REU-N3237FF-US), RU180i (REU-N2934FF-US), RU160i (REU-N2530FF-US), RU130i (REU-N2024FF-US), RU199e (REU-N3237W-US), RU180e (REU-N2934W-US), RU160e (REU-N2530W-US), RU130e (REU-N2024W-US) |
| SENSEI residential with pump | RUR199i (REU-NP3237FF-US), RUR160i (REU-NP2530FF-US), RUR199e (REU-NP3237W-US), RUR160e (REU-NP2530W-US) |
Where this comes from
- Error codes for gas continuous flow water heaters (HW Gas CF ERR) , page 3
- Infinity gas continuous flow operation and installation manual , page 12
- Infinity Enviro 32 / HDC32 operation and installation manual , page 12
- Troubleshooting tankless water heater diagnostic codes (100000652), non-SENSEI and SENSEI series , page 28
- N Series residential condensing installation and operation manual (100000467), RU199e/RU180e/RU160e/RU130e , page 60
Checked against the manufacturer's manual on 9 October 2026.
Other Rinnai tankless water heater codes
| Code | Meaning | What you can do |
|---|---|---|
| 14 | Overheat safety device tripped | Call a pro |
| 15 | Venturi control failure | Safe checks first, then a pro |
| 16 | Over-temperature shutdown | Safe checks first, then a pro |
| 17 | Venturi blockage | Safe checks first, then a pro |
| 18 | Gas valve adjustment limit | Call a pro |
| 19 | Electrical earth fault | Call a pro |
| 22 | Gas valve adjustment fault | Call a pro |
| 25 | Sensor fault or condensate blockage (depends on model) | Depends on your model |
| 32 | Outgoing water temperature sensor fault | Call a pro |
| 33 | Heat exchanger thermistor fault | Call a pro |
| 34 | Temperature sensor fault (depends on model) | Call a pro |
| 36 | Lower tank thermistor fault | Call a pro |
See all configuration error codes on tankless water heaters across brands.