31
Noritz
Inlet Thermistor Failure
Boiler will not start and shows error 31 on the display.
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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 control board
How to Fix / Troubleshooting
Safety: Turn OFF power before accessing internal wiring.
- 1. Locate inlet thermistor: Remove the front cover and find the cold water inlet thermistor on the inlet pipe of the Noritz boiler.
- 2. Inspect wiring: Check the thermistor leads for cuts, burns, or pulled wires. Ensure the connector is fully seated on the control board.
- 3. Clean connectors: If there is light corrosion, disconnect power, unplug the connector, and clean contacts with electrical contact cleaner. Reconnect firmly.
- 4. Replace thermistor if needed: If the wiring is intact but error 31 persists, the thermistor is likely defective. Replacement requires draining the boiler and installing a new Noritz inlet thermistor; this is best done by a qualified technician.
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Repair Difficulty
Medium
3/5
Required Part
Inlet Thermistor
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