F2
Bosch
Return NTC Fault
Boiler indicates a return temperature sensor fault; may cause poor modulation or lockout.
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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 return NTC, Loose sensor clip, Wiring harness damage, PCB sensor input failure
How to Fix / Troubleshooting
Safety: Isolate power and let the boiler cool.
Steps:
- Check that the return NTC is firmly attached to the return pipe.
- Inspect and reseat the wiring connectors.
- Test the NTC resistance and replace if faulty.
Persistent faults after sensor replacement require PCB diagnosis by a technician.
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Repair Difficulty
Medium
3/5
Required Part
Return NTC Temperature Sensor
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