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

1. Inspect the harness from the burner overheat bi-metal switch to the PC board for loose, broken or damaged connections.
2. Confirm the heater's gas type matches the supply (e.g., a natural gas unit on natural gas).
3. Warning: Only a person qualified to service gas systems should perform the following gas checks.
4. Check low and high fire manifold pressures using the gas pressure setting procedure for the installation's elevation.
5. 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.
6. Warning: Disconnect power to the heater, then replace the bi-metal sensor.
7. After correcting the fault, hard reset by turning power off and back on.
8. 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
• RUCS/RUS water quality limits · Non-SENSEI