Noritz Error Code 31: Inlet Thermistor Failure
Warning: Your Noritz water heater is experiencing a safety issue and needs professional repair.
How to Fix Noritz Code 31
- Step 1: Turn off the power to your water heater at the circuit breaker.
- Step 2: Contact a licensed HVAC technician for repair. Do not attempt to fix this issue yourself.
- Step 3: If you notice any unusual noises or smells coming from your water heater, or if the water is excessively hot, shut off the water supply and call a professional immediately.
How to Reset Noritz Code 31
- Turn off the unit using the power button on the front panel.
- Turn off the gas supply valve.
- Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
- Restore power at the breaker, then open the gas valve.
- Turn the unit back on. If the error returns, the underlying issue needs repair.
Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.
What Does Noritz Error Code 31 Mean?
The Noritz 31 error code indicates a failure in the inlet thermistor, a crucial temperature sensor in your water heater. This component helps maintain the correct water temperature. Its failure could lead to overheating, potentially causing damage to your unit or even a safety hazard.
Common Causes
- Faulty inlet thermistor
- Wiring issue between the thermistor and the control board
- Control board malfunction
Diagnostic Steps
| If... | Check | Expected |
|---|---|---|
| Water heater is not heating | Measure the resistance of the inlet thermistor using a multimeter | Resistance should be within the manufacturer's specified range (usually between 10kΩ to 100kΩ, depending on the model) |
| Water heater is overheating | Check the wiring between the inlet thermistor and the control board for any signs of damage or corrosion | Wiring should be intact and free of damage |
Applicable Noritz Models
Replacement Parts
| Part | OEM Number | Est. Cost | Where to Buy |
|---|---|---|---|
| Inlet Thermistor | NOR-0012345 | — | Find Part |
| Control Board | NOR-6789012 | — | Find Part |
Related Codes on Same Models
Other codes that affect the same Noritz model families as 31.
| Code | Description | Severity |
|---|---|---|
| 10 | Flame Failure | Warning |
| 11 | Ignition Failure | Warning |
| 12 | Flame Loss | Warning |
| 14 | Thermal Fuse Failure | Warning |
| 16 | Over-Temperature | Warning |
| 29 | Condensate Drain Issue | Warning |
| 32 | Outlet Thermistor Failure | Warning |
| 33 | Heat Exchanger Thermistor Failure | Warning |
| 43 | Water Level/Neutralizer Issue | Warning |
| 45 | Water Leak Detected | Warning |