Rinnai Flame Sensing Circuit Abnormality

Boiler intermittently locks out with error 72, often during ignition attempts.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Intermittent flame rod connection, Poor grounding of boiler, Electrical noise on flame circuit, Failing control PCB

Safety first: Isolate power and gas before working inside the boiler.

Check flame rod connection: Ensure the flame rod lead is tight and free of corrosion at both the rod and PCB ends.
Verify earth/ground: Confirm that the boiler chassis is solidly grounded to the building earth.
Reduce electrical noise: Avoid routing high-voltage or motor cables alongside the flame sensor wiring.
Reset and observe: Restore power and reset the boiler. If error 72 recurs, a technician should test the flame circuit and likely replace the control PCB.

Hard 4/5

Flame Rod (Flame Sensor)

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