HVACopediaRinnai · Tankless water heater
57 Burner overheat bi-metal switch open
What the control is telling you
One of the two bi-metal switches at the back of the burner assembly has opened. The code shows whether or not the unit is running and clears only after the fault is fixed and power is cycled (hard reset).
Applies to: Non-SENSEI Series (KB Series condensing: see Technical Bulletin 107)
Likely causes
- Loose, broken or damaged bi-metal switch wiring
- Heater connected to the wrong gas type
- Low/high fire manifold pressures set incorrectly
- Improper gas conversion (pressures or DIP switches not matched)
- Failed bi-metal sensor
Test and repair steps
- Inspect the harness from the burner overheat bi-metal switch to the PC board for loose, broken or damaged connections.
- Confirm the heater's gas type matches the supply (e.g., a natural gas unit on natural gas).
- Warning: Only a person qualified to service gas systems should perform the following gas checks.
- Check low and high fire manifold pressures using the gas pressure setting procedure for the installation's elevation.
- If the unit was ever converted to another gas type, confirm the conversion followed the manufacturer's instructions and that pressures and DIP switches match the new gas.
- Warning: Disconnect power to the heater, then replace the bi-metal sensor.
- After correcting the fault, hard reset by turning power off and back on.
- KB Series condensing units refer to Rinnai Technical Bulletin 107 for troubleshooting codes 14 and 57.
Settings for these units
RUCS/RUS unit clearances · Non-SENSEI
| Location | RUCS indoor to combustibles | RUCS indoor to non-combustibles | RUS outdoor to combustibles | RUS outdoor to non-combustibles |
|---|---|---|---|---|
| Top | 6 in. (152 mm) * | 2 in. (51 mm) * | 12 in. (305 mm) | 2 in. (51 mm) |
| Back | 0 in. | 0 in. | 0 in. | 0 in. |
| Front | 6 in. (152 mm) | 6 in. (152 mm) | - | - |
| Front (panel) | - | - | 24 in. (610 mm) | 0 in. |
| Front (exhaust) | - | - | 24 in. (610 mm) | 24 in. (610 mm) |
| Sides | 2 in. (51 mm) | 1/2 in. (13 mm) | 6 in. (152 mm) | 1/8 in. (3.2 mm) |
| Ground/bottom | 12 in. (305 mm) | 12 in. (305 mm) | 12 in. (305 mm) | 2 in. (51 mm) |
| Vent | 0 in. | 0 in. | - | - |
0 in. from vent components and condensate drain line.
Service clearance 24 in. in front of the heater; closet installs need 6 in. (152 mm) in front.
RUCS/RUS water quality limits · Non-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 or PPM |
| 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 |
Scale build-up shows as code LC# on a controller (LC on the status monitor without one); flush the heat exchanger.
ScaleCutter parts: 103000038 (system), 103000039 (refill).
Models that show this code
59 models in Non-SENSEI, RH180 hybrid
Other codes on the same units
- 41 Freeze protection / outdoor air temperature sensor fault
- 51 Inlet water temperature thermistor fault
- 52 Gas valve / modulating solenoid valve (POV) signal fault
- 54 High exhaust gas temperature
- 58 Secondary heat exchanger bi-metal switch open
- 61 Combustion fan motor fault
- 63 Recirculation low flow
- 65 Water flow control device (servo) fault
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Source: Rinnai Troubleshooting TWH Diagnostic Codes (100000652), p.50. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
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.