Applicable Systems
Baxi Heating Boiler
Symptoms
The Baxi boiler displays fault code BX008, indicating a temperature sensor fault. The NTC thermistor on the flow or return pipe is reading outside its valid range, causing inaccurate temperature control.
Possible Causes
- NTC thermistor has drifted from its calibrated resistance-temperature curve due to aging
- Sensor wiring has developed high resistance or a loose connection at the terminal block
- Sensor is physically damaged from a water leak that has corroded the sensor housing or wiring
Troubleshooting Steps
- Step 1: Measure the sensor resistance at the current temperature and compare to the specification table
Resistance matches the expected value for the measured temperature within 5 percent tolerance - Step 2: Check the sensor wiring and terminal connections for looseness or corrosion
All connections are tight, clean, and the wiring shows no signs of corrosion or damage - Step 3: Inspect the sensor housing and the surrounding pipe for water leak damage
No water damage is present and the sensor housing is intact and dry
How to Reset
To reset: 1) Replace the faulty NTC thermistor with a new calibrated sensor. 2) Repair wiring and connections. 3) Press RESET. 4) Verify the boiler maintains the setpoint temperature accurately.
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Source: Baxi Boiler Manual, Baxi Heating UK Ltd
Category: Home Boiler
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