Rinnai RH180 Installation Fundamentals page 57

Maintenance Codes
Code Definition
72 Flame sensing
device.
73 Burner sensor
circuit.
No No hot water, no
code light or error code
on display.
57
Remedy
Licensed
Verify flame rod is touching flame when it fires.
professional
Check all wiring to flame rod.
only
Remove flame rod and check for carbon buildup.
Check inside burner chamber for any foreign material blocking flame at flame
rod.
Measure micro-amp output of sensor circuit with flame present.
Replace flame rod.
Replace PCB.
Licensed Check sensor wiring and PCB for damage.
professional
Replace sensor.
only
Replace PCB.
Confirm the water heater is plugged in and has 120 VAC available.
Confirm the water heater is turned on at the temperature controller.