33
Noritz
Heat Exchanger Thermistor Fault
Error code 33 appears; unit may not modulate correctly or may shut down.
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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
Failed heat exchanger thermistor, Broken or shorted sensor wiring, Poor connection at PCB, Overheating damage to sensor
How to Fix / Troubleshooting
Safety first: Turn OFF power and gas. Allow the unit to cool completely before touching the heat exchanger area.
Steps to check and correct:
- Locate heat exchanger thermistor: This sensor is mounted directly on or near the heat exchanger body. Refer to your Noritz service manual for exact location.
- Inspect wiring and connector: Check for heat-damaged insulation, loose plugs, or corrosion. Reseat connectors.
- Test thermistor: With a multimeter, measure resistance and compare to Noritz temperature-resistance chart. Replace the thermistor if out of range.
- Check for overheating causes: If the sensor shows signs of heat damage, investigate for scale buildup, blocked vents, or pump/flow issues that may have caused excessive temperatures.
- Reset and test: Restore power and run the unit. If error 33 persists, the PCB may need replacement by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Heat Exchanger Thermistor
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