Rinnai tankless water heater code 79: Water leak detected
Tankless water heater, United States
The leak sensor inside the cabinet detected water.
This needs a licensed gas or HVAC technician. There are a few safe checks you can do first, marked below. Anything inside the unit is a job for a professional.
Water may be leaking. Turn off the water supply to the unit if you see a leak.
Only some models show this code. Check the list below.
What causes it
-
A leak from the heat exchanger or internal piping.
Stop the water if it will not turn offYou can do this
- Turn off the tap or stop the bath fill straight away.
- If water keeps running or leaking, close the cold water isolation valve to the unit, or the main water valve to the house.
- Do not use the unit or the bath fill function again until it has been serviced.
-
A wet leak sensor or a faulty sensor.
How to read this code on your unit
Booking a licensed gas or HVAC technician
Book a licensed gas or HVAC technicianlicensed gas or HVAC 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 or HVAC 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
32 models in 7 ranges
| Range | Models |
|---|---|
| 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) |
| 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
- Troubleshooting tankless water heater diagnostic codes (100000652), non-SENSEI and SENSEI series , page 54
Checked against the manufacturer's manual on 9 October 2026.
Other Rinnai tankless water heater codes
| Code | Meaning | What you can do |
|---|---|---|
| 58 | Secondary heat exchanger overheat | Call a pro |
| 61 | Combustion fan failure | Call a pro |
| 63 | Recirculation low flow | 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 |
| 92 | Neutraliser end of life | Call a pro |
| LC | Scale build-up in the heat exchanger | Safe checks first, then a pro |
| SE | Cascade connection failure | Call a pro |