Rinnai code 63: Recirculation low flow
Continuous flow hot water system (Australia), tankless water heater (United States)
Flow in the hot water recirculation loop is too low.
This needs a licensed gas technician. There is nothing safe to check yourself. Leave the covers on and book a professional.
What causes it
Australian models
-
Low flow in the recirculation loop. Rinnai lists this as needing a service call.
US models
-
Air in the recirculation line, or clogged inlet and bypass filters.
-
Closed isolation valves, the bypass plug or filter set up for the wrong recirculation mode, or wrong recirculation parameters.
-
A leak in the home's plumbing letting the pump draw in air.
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.
Book a licensed plumberplumber
- Note the code, the model and serial numbers, and what the system was doing when the code appeared.
- Book a licensed plumber and give them those details.
Models that show this code
54 models in 12 ranges
| Range | Models |
|---|---|
| Heavy Duty (commercial) | REU-NB3237WC-AK (Heavy Duty 32C), REU-NB3237FFC-AK, REU-NB3237WC-50-AK, REU-NB3237FFC-50-AK |
| Infinity Enviro | REU-NB3237W-AK (Infinity Enviro 32), REU-NB3237W-50-AK |
| Commercial (KB) | C199i (REU-KBD3237FFUDC-US), C199e (REU-KB3237WDC-US) |
| KB | RU80i (REU-KB2530FFUD-US), RU80e (REU-KB2530WD-US), RU90e (REU-KBD2934WD-US), RU98i (REU-KB3237FFUD-US), RU98e (REU-KB3237WD-US) |
| KBD | RUC80i (REU-KBD2530FFUD-US), RUC90i (REU-KBD2934FFUD-US), RUC98i (REU-KBD3237FFUD-US) |
| KBP | RUR98i (REU-KBP3237FFUD-US), RUR98e (REU-KBP3237WD-US) |
| KCM | RUCS65i (REU-KCM2025FFU-US), RUCS75i (REU-KCM2528FFU-US), RUS65e (REU-KCM2025W-US), RUS75e (REU-KCM2528W-US) |
| Luxury (VC) | RL75i (REU-VC2528FFUD-US), RL75i(A) (REU-VC2528FFUD-US(A)), RL75e (REU-VC2528WD-US), RL75e(A) (REU-VC2528WD-US(A)), RL94i (REU-VC2837FFUD-US), RLX94i (REU-VC2737FFUD-US), RL94e (REU-VC2837WD-US) |
| 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) |
| Value (VC) | V53e (REU-VAM1620W-US), V53De (REU-AM1620WD-US), V65i (REU-VC2025FFU-US), V65e (REU-VC2025W-US), V75i (REU-VC2528FFU-US), V75e (REU-VC2528W-US), V94i (REU-VC2837FFU-US), V94Xi (REU-VC2737FFU-US), V94e (REU-VC2837W-US) |
Where this comes from
- Infinity Enviro 32 / HDC32 operation and installation manual , page 12
- Troubleshooting tankless water heater diagnostic codes (100000652), non-SENSEI and SENSEI series , page 46, 47
- 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 |
|---|---|---|
| 52 | Gas modulating valve fault | Call a pro |
| 54 | High exhaust gas temperature | Safe checks first, then a pro |
| 55 | Service reminder | Safe checks first, then a pro |
| 57 | Burner overheat switch open | Call a pro |
| 58 | Secondary heat exchanger overheat | Call a pro |
| 61 | Combustion fan failure | Call a pro |
| 65 | Water flow control failure | Safe checks first, then a pro |
| 66 | Bypass flow control fault | Call a pro |
| 70 | Control board (PCB) failure | Safe checks first, then a pro |
| 71 | Gas solenoid valve failure | Call a pro |
| 72 | Flame rod circuit error | Call a pro |
| 73 | Burner thermocouple fault | Call a pro |