31
Noritz Inlet Thermistor Fault

Error code 31 displayed; unit may not start or may shut down shortly after startup.

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Safety Warning

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.

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Possible Causes

Open or shorted inlet thermistor, Damaged thermistor wiring harness, Corroded connector at PCB, Incorrect resistance due to sensor failure

How to Fix / Troubleshooting

Safety first: Turn OFF power and gas before removing the front cover.

Steps to check and correct:

  • Locate inlet thermistor: Find the inlet water temperature sensor on the cold water side of the Noritz unit. It is typically a small probe with two wires.
  • Inspect wiring and connector: Check for frayed wires, pinched insulation, or loose connectors. Reseat the connector at both the sensor and PCB ends.
  • Check sensor resistance (advanced): Using a multimeter and the Noritz service manual, measure the thermistor resistance at room temperature and compare to the specified value. If readings are far off, replace the inlet thermistor.
  • Reset and test: Restore power and run hot water. If error 31 remains, the PCB input circuit may be defective and should be evaluated by a professional.
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Repair Difficulty

Medium 3/5

Required Part

Inlet Thermistor
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