33
Rinnai
Heat Exchanger Thermistor Fault
Boiler shows error 33; unit may lock out immediately on a call for heat or hot water.
Advertisements
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.
Advertisements
Possible Causes
Defective heat exchanger thermistor, Thermistor dislodged from heat exchanger, Wiring harness damage, Control board sensor circuit failure
How to Fix / Troubleshooting
Safety first: Isolate power and gas. The heat exchanger area can remain hot for some time after shutdown.
- Access thermistor: Remove the front cover and locate the thermistor mounted directly on or near the primary heat exchanger body.
- Check mounting: Ensure the thermistor is firmly attached and making good thermal contact with the heat exchanger surface.
- Inspect wiring: Look for signs of overheating, brittleness, or mechanical damage along the thermistor cable.
- Reconnect and test: Reseat the connector at the control board, restore power, and reset the boiler. If error 33 persists, replace the thermistor.
- Further diagnosis: If a new thermistor does not clear the fault, a technician should test the control PCB.
Advertisements
Repair Difficulty
Medium
3/5
Required Part
Heat Exchanger Thermistor
Check Price on Amazon
We may earn a commission from links on this page.
Advertisements