Rinnai tankless water heater code 57: Burner overheat switch open
Tankless water heater, United States
One of the two overheat switches on the back of the burner opened. The code shows whether or not the heater is running and needs a power reset once fixed.
This needs a licensed gas or HVAC technician. There is nothing safe to check yourself. Leave the covers on and book a professional.
This involves the gas supply or burner. Only a licensed technician should open the unit or work on gas parts.
Only some models show this code. Check the list below.
What causes it
-
The heater is connected to the wrong gas type, was converted incorrectly, or has manifold pressures set wrong.
-
Damaged switch wiring or a failed overheat switch.
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.
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 43
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 |
| 38 | Exhaust temperature thermistor fault | Call a pro |
| 41 | Frost protection (ambient) sensor fault | Call a pro |
| 51 | Inlet water thermistor fault | Call a pro |
| 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 |
| 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 |
See all overheat codes on tankless water heaters across brands.