33
Noritz
Heat Exchanger Thermistor Failure
Boiler shows error 33 and stops heating.
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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
Defective heat exchanger thermistor, Damaged wiring harness, Poor contact at control board
How to Fix / Troubleshooting
Safety: Turn OFF power before opening the boiler cabinet.
- 1. Identify sensor: Refer to the Noritz service manual to locate the heat exchanger thermistor mounted on or near the primary heat exchanger.
- 2. Inspect harness: Check for chafed wires, loose connectors, or signs of overheating around the sensor.
- 3. Reseat connector: Unplug the thermistor connector from the control board (with power OFF), inspect for corrosion, and reconnect firmly.
- 4. Professional replacement: If error 33 persists, the thermistor is likely out of range and must be replaced with a Noritz part by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Heat Exchanger Thermistor
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